Systems and Methods to Recover Value-Added Materials from Gypsum

ABSTRACT

Disclosed herein are systems and methods from processing flue gas desulfurization (FGD) gypsum feedstock and ash feedstocks, either separately or together. FGD gypsum conversion comprises reacting FGD gypsum (calcium sulfate) feedstock or phosphogypsum, in either batch or continuous mode, with ammonium carbonate reagent to produce commercial products comprising ammonium sulfate and calcium carbonate. A process to separate the impurities and convert the calcium carbonate to a pure precipitated calcium carbonate is disclosed. These impurities include a concentrate of valuable Rare Earth Elements, and radioactive thorium and uranium. A process to convert calcium sulfite to calcium sulfate using oxygen and a catalyst is also disclosed. Ash conversion comprises a leach process followed by a sequential precipitation process to selectively precipitate products at predetermined pHs resulting in metal hydroxides which may be converted to oxides or carbonates. The processes may be controlled by use of one or more processors.

RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 17/321,437, entitled Systems and Methods to RecoverValue-Added Materials from Gypsum, filed May 15, 2021, which takespriority to U.S. patent application Ser. No. 63/025,548, entitledSystems and Methods to Oxidize Calcium Sulfite From Flue GasDesulfurization Scrubbers to Calcium Sulfate, filed May 15, 2020, and toU.S. patent application Ser. No. 63/149,045 entitled Systems and Methodsto Recover Value-Added Materials from Gypsum, filed Feb. 12, 2021; whichalso is a continuation-in-part of U.S. patent application Ser. No.16/749,860, entitled Systems and Methods to Treat Flue GasDesulfurization Waste to Produce Ammonium Sulfate and Calcium CarbonateProducts, filed Jan. 22, 2020, now U.S. Pat. No. 11,148,956, issued Oct.19, 2021, which takes priority to U.S. patent application Ser. No.62/878,542, entitled Systems and Methods for Pretreatment of FeedstocksComprising Sulfites, filed Jul. 25, 2019, U.S. patent application Ser.No. 62/824,523, entitled Reducing the Cost of Reagents for TreatingMetal Bearing Wastes, filed Mar. 27, 2019, U.S. patent application Ser.No. 62/810,066, entitled Removal of Chloride from Flue GasDesulfurization Feed, filed Feb. 25, 2019, and U.S. patent applicationSer. No. 62/796,541, entitled Systems and Methods to Treat Flue GasDesulfurization (FGD) Waste to Produce High Purity Ammonium Sulfate andCalcium Carbonate Products, filed Jan. 24, 2019, the entire contents ofwhich are incorporated herein by reference. This application is relatedto U.S. patent application Ser. No. 62/796,549, entitled Systems andMethods to Chemically Treat Metal-bearing Waste Streams to RecoverValue-added Materials, filed Jan. 24, 2019, U.S. patent application Ser.No. 62/796,550, entitled Systems and Methods to Chemically TreatMetal-bearing Waste Streams to Recover Value-added Materials, filed Jan.24, 2019, U.S. patent application Ser. No. 16/749,860 entitled Systemsand Methods to Treat Flue Gas Desulfurization Waste to Produce HighPurity Ammonium Sulfate and Calcium Carbonate Products, filed Jan. 22,2020, and U.S. patent application Ser. No. 16/752,477 entitled Systemsand Methods to Chemically Treat Metal-Bearing Waste Streams to RecoverValue-Added Materials, filed Jan. 24, 2020, PCT App. No.PCT/US2020/015102 entitled Systems and Methods to Treat Flue GasDesulfurization and Metal-Bearing Waste Streams to Recover Value-AddedMaterials, filed Jan. 24, 2020, the entire contents of which areincorporated herein by reference. The above-incorporated materialconstitutes “essential material” within the meaning of 37 CFR1.57(d)(1)-(3), applicant(s) have included the specification toexpressly recite the essential material that is incorporated byreference as allowed by the applicable rules.

COPYRIGHT NOTICE

Contained herein is material that is subject to copyright protection.The copyright owner has no objection to the facsimile reproduction byanyone of the patent document or the patent disclosure, as it appears inthe United States Patent and Trademark Office patent file or records,but otherwise reserves all rights to the copyright whatsoever. Thefollowing notice applies to the software, screenshots and data asdescribed below and in the drawings hereto and All Rights Reserved.

TECHNICAL FIELD

This disclosure relates generally to chemical processing of CoalCombustion Products (CCP) and phosphoric acid production waste toproduce value-added, marketable products while simultaneously minimizingor eliminating one or more resultant waste streams.

BACKGROUND

Coal combustion products (CCP) comprise fly ash (fine particulatescollected in electrostatic precipitators), lime or limestone from anabsorption spray tower, which separates out sulfur oxide (SO_(x)) gases,and bottom ash which remains after coal combustion. The lime orlimestone in the absorption bed reacts with the SO_(x) gases resultingin calcium sulfite (hannebachite, CaSO₃.0.5H₂O). The calcium sulfite isoften oxidized to calcium sulfate, which is referred to as flue gasdesulfurization (FGD) gypsum. In some coal plants, the calciumsulfite/sulfate byproduct is separated from the other byproducts whilein others it is mixed in with the ash.

Currently, the primary applications of calcium sulfate (CaSO₄) or FGDgypsum are in the wallboard industry and as a soil amendment. The flyash is commonly used in the construction industry as a cement additive.However, significant portions of FGD gypsum and ash are not marketable;thus, they are stored in piles and ponds, and present a plethora ofenvironmental issues.

Many efforts have focused on utilizing specific components of CCPs, suchas converting calcium sulfate to ammonium sulfate fertilizer and calciumcarbonate filler. Others have attempted to extract specific elements outof the CCPs, such as aluminum or rare earth elements. To date there hasnot been a successful effort to treat the entire inventory and convertit to value-added, marketable products with minimal or no waste.

Phosphogypsum (PG) refers to the calcium sulfate hydrate formed as aby-product of the production of fertilizer from phosphate rock. It ismainly composed of gypsum (CaSO₄.2H₂O). Although gypsum is a widely usedmaterial in the construction industry, phosphogypsum is usually notused; rather, it is stored indefinitely because of its weakradioactivity. The long-duration storage is controversial. Somewherebetween 100,000,000 and 280,000,000 tons are estimated to be producedannually as a consequence of processing phosphate rock for theproduction of phosphate fertilizers. Phosphogypsum is a side-productfrom the production of phosphoric acid (FIG. 61 ) by treating phosphateore (apatite) with sulfuric acid according to the following reaction(1):

Ca₅(PO₄)₃X+5H₂SO₄+10H₂O→3H₃PO₄+5(CaSO₄.2H₂O)+HX   (1)

where X may include OH, F, Cl, or Br.

Phosphogypsum is radioactive due to the presence of naturally occurringuranium and thorium, and their daughter isotopes radium, radon, etc. Inaddition, many phosphate deposits contain several hundreds of parts permillion of valuable rare earth elements. Marine-deposited phosphatetypically has a higher level of radioactivity than igneous phosphatedeposits, because uranium is present in seawater. Other components of PGare cadmium (5-28 ppm), fluoride (ca 1%), and silica. The United StatesEnvironmental Protection Agency has banned most applications ofphosphogypsum having a ²²⁶Ra concentration of greater than 10picocurie/gram (0.4 Bq/g). As a result, phosphogypsum that exceeds thislimit is stored in large stacks.

Central Florida has a large quantity of phosphate deposits, particularlyin the Bone Valley region; many PG stacks are located near Fort Meade,Fla. However, the marine-deposited phosphate ore from central Florida isweakly radioactive, and as such, the phosphogypsum by-product (in whichthe radionuclides are somewhat concentrated) is too radioactive to beused for most applications. As a result, there are about 1 billion tonsof phosphogypsum stacked in 25 stacks in Florida (22 are in centralFlorida) and about 30 million new tons are generated each year.

What is needed are methods for treating whole stocks of FGD gypsum andPG to reduce waste and produce marketable products.

SUMMARY

Disclosed herein are systems and methods for processing flue gasdesulfurization (FGD) gypsum feedstock and ash feedstocks, eitherseparately or together, as well as other gypsum feedstocks such asphosphogypsum. FGD gypsum conversion comprises reacting FGD gypsum(calcium sulfate) feedstock, in either batch or continuous mode, with anammonium carbonate reagent to produce commercial products comprisingammonium sulfate and calcium carbonate. Similarly, phosphogypsum (PG),which is a byproduct of phosphoric acid production, can be processed ina similar manner to produce ammonium sulfate and calcium carbonatehaving similar applications. This is covered in more detail in thesection “PHOSPHOGYPSUM CONVERSION SYSTEMS AND METHODS”. Ash conversioncomprises a leach process followed by a precipitation process toselectively precipitate components at one or more predetermined pHsresulting in metal hydroxides, which may be optionally converted tooxides or carbonates. The processes may be controlled by use of one ormore processors.

An exemplary embodiment of the disclosure is a system comprising acalcium sulfate feedstock comprising calcium sulfate and at least twoimpurities; a mixer to combine ammonia gas, carbon dioxide, and water,resulting in an ammonium carbonate reagent solution; one or more firstreactors to combine and react the calcium sulfate feedstock with theammonium carbonate reagent solution; the reaction forming a firstreacted slurry, comprising calcium carbonate, ammonium sulfate, and theat least two impurities; a first filter to separate the calciumcarbonate and the at least two impurities from the first reacted slurry,producing an ammonium sulfate filtrate; an evaporator to evaporate waterfrom the ammonium sulfate filtrate to produce an ammonium sulfateliquor; a crystallizer to crystallize and agglomerate the ammoniumsulfate liquor, resulting in ammonium sulfate crystals; a centrifuge toseparate the ammonium sulfate crystals from the ammonium sulfate liquor;a dryer to dry the ammonium sulfate crystals; a second reactor tocombine and dissolve the calcium carbonate and the at least twoimpurities with a solvent, resulting in a second reacted slurry, thesecond reacted slurry comprising solutes of the at least two impurities,calcium, and at least one insoluble component; a second filter toseparate the at least one insoluble component from the second liquor,resulting in a second filtrate comprising the solutes of the at leasttwo impurities and the calcium nitrate, wherein the second filtrate hasa pH; a third reactor to combine the second filtrate with a first baseto precipitate a first metal from the second filtrate, wherein the firstbase is added until the pH of the second filtrate increases to a firstpredetermined pH, and wherein the first metal is at least one of the atleast two impurities; a third filter to separate the first metal fromthe second filtrate, resulting in a third filtrate comprising thecalcium and a solute of the second of the at least two impurities,wherein the third filtrate has a pH; a fourth reactor to combine thethird filtrate with a second base to precipitate a second metal from thethird filtrate, wherein the second base is added until the pH of thethird filtrate increases to a second determined pH, wherein the secondmetal is the second of the at least two impurities; a fourth filter toseparate the second metal from the third filtrate, resulting in a fourthfiltrate comprising the calcium; a fifth reactor to combine the fourthfiltrate with a soluble carbonate to precipitate calcium carbonate fromthe fourth filtrate, wherein the soluble carbonate is added until the pHof the fourth filtrate increases to a third predetermined pH; and afifth filter to separate the calcium carbonate from the fourth filtrate.

Applicant(s) herein expressly incorporate(s) by reference all of thefollowing materials identified in each paragraph below. The incorporatedmaterials are not necessarily “prior art”.

U.S. patent application Ser. No. 15/669,870, entitled System and Methodfor Distributed Trading Platform, filed Aug. 4, 2017, hereinincorporated by reference in its entirety.

U.S. patent application Ser. No. 15/675,697, entitled Systems andMethods for Using Smart Contracts to Control the Trade, Supply,Manufacture, and Distribution of Commodities, filed Aug. 11, 2017,herein incorporated by reference in its entirety.

If it is believed that any of the above-incorporated materialconstitutes “essential material” within the meaning of 37 CFR1.57(d)(1)-(3), applicant(s) reserve the right to amend thespecification to expressly recite the essential material that isincorporated by reference as allowed by the applicable rules.

Aspects and applications presented here are described below in thedrawings and detailed description. Unless specifically noted, it isintended that the words and phrases in the specification and the claimsbe given their plain, ordinary, and accustomed meaning to those ofordinary skill in the applicable arts. The inventors are fully awarethat they can be their own lexicographers if desired. The inventorsexpressly elect, as their own lexicographers, to use only the plain andordinary meaning of terms in the specification and claims unless theyclearly state otherwise and then further, expressly set forth the“special” definition of that term and explain how it differs from theplain and ordinary meaning. Absent such clear statements of intent toapply a “special” definition, it is the inventors' intent and desirethat the simple, plain, and ordinary meaning to the terms be applied tothe interpretation of the specification and claims.

Further, the inventors are informed of the standards and application ofthe special provisions of 35 U.S.C. § 112(f). Thus, the use of the words“function,” “means”, or “step” in the Detailed Description orDescription of the Drawings or claims is not intended to somehowindicate a desire to invoke the special provisions of 35 U.S.C. § 112(f)to define the systems, methods, processes, and/or apparatuses disclosedherein. To the contrary, if the provisions of 35 U.S.C. § 112(f) aresought to be invoked to define the embodiments, the claims willspecifically and expressly state the exact phrases “means for” or “stepfor” and will also recite the word “function” (i.e., will state “meansfor performing the function of . . . ”), without also reciting in suchphrases any structure, material, or act in support of the function.Thus, even when the claims recite a “means for performing the functionof . . . ” or “step for performing the function of . . . ”, if theclaims also recite any structure, material, or acts in support of thatmeans or step, then it is the clear intention of the inventors not toinvoke the provisions of 35 U.S.C. § 112(f). Moreover, even if theprovisions of 35 U.S.C. § 112(f) are invoked to define the claimedembodiments, it is intended that the embodiments not be limited only tothe specific structures, materials, or acts that are described in thepreferred embodiments, but in addition, include any and all structures,materials, or acts that perform the claimed function as described inalternative embodiments or forms, or that are well known present orlater-developed equivalent structures, materials, or acts for performingthe claimed function.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the systems, methods, processes, and/orapparatuses disclosed herein may be derived by referring to the detaileddescription when considered in connection with the followingillustrative figures. In the figures, like-reference numbers refer tolike-elements or acts throughout the figures.

FIG. 1 depicts a system and method for combining an FGD gypsumconversion process with an ash conversion process.

FIG. 2 depicts an embodiment of a production plant for implementing anFGD gypsum conversion process.

FIG. 3 is a table showing the composition of an FGD gypsum feedstockused in testing.

FIG. 4 depicts a particle size distribution analysis for the FGD gypsumfeedstock used in testing.

FIG. 5 depicts kinetic data for varying reagent stoichiometric additionsin testing of the FGD gypsum conversion process.

FIG. 6 depicts crystallized ammonium sulfate product assays for productgenerated in testing of the FGD conversion process.

FIG. 7 depicts example test conditions and results from testing of theFGD conversion process.

FIG. 8 depicts calculated final product purity generated in testing ofthe FGD conversion process.

FIG. 9 depicts a schematic of a pilot production plant operating incontinuous mode.

FIG. 10 depicts calculated gypsum conversion rates with differentstoichiometric conditions in the pilot production plant depicted in FIG.9 .

FIG. 11 depicts discharge sulfur assays from the pilot production plantdepicted in FIG. 9 showing the reaction times as a function ofstoichiometry.

FIG. 12 depicts exemplary ammonium sulfate and calcium carbonateproducts produced by the pilot production plant depicted in FIG. 9 .

FIG. 13 depicts a composition of an ammonium sulfate product produced bythe pilot production plant depicted in FIG. 9 .

FIG. 14 depicts an embodiment of a calcium sulfite oxidation processadded to FIG. 2 to treat the FGD gypsum feedstock prior to feeding intothe FGD gypsum conversion process.

FIG. 15 depicts an embodiment of an acid dissolution calcium carbonatewhitening process.

FIG. 16 depicts a whitened calcium carbonate product produced by thecalcium carbonate whitening process depicted in FIG. 15 .

FIG. 17 depicts an example embodiment of a process for using a catalystto separate impurities from calcium carbonate product produced by theFGD conversion process.

FIG. 18 depicts a lime embodiment of an ash conversion system andprocess.

FIG. 19 is a continuation of the FIG. 18 flowsheet.

FIG. 20 depicts a caustic embodiment of an ash conversion system andprocess.

FIG. 21 is a continuation of the FIG. 20 flowsheet.

FIG. 22 is a table depicting the major earth forming oxides of a class Fand a class C ash feedstock used in preliminary testing of the ashconversion process.

FIG. 23 is a table depicting the major, minor, and trace elementalcomposition of the class F and class C ash feedstocks used inpreliminary testing of the ash conversion process.

FIG. 24 is a table depicting mineralogical composition of the class Fand class C ash feedstocks used in preliminary testing of the ashconversion process.

FIG. 25 is a table depicting leaching results of class F and class C ashfeedstocks using 3:1 hydrochloric acid to nitric acid.

FIG. 26 is a table depicting leaching results of class F and class C ashusing sulfuric acid and sodium fluoride.

FIG. 27 is a table depicting leaching results of class F and class C ashfeedstock using sulfuric acid and calcium fluoride.

FIG. 28 is a table depicting leaching results of class F and class C ashfeedstock using hydrochloric acid in two stages starting withhydrochloric acid at pH 1.5 followed by 11% hydrochloric acid.

FIG. 29 is a table depicting leaching results of class F and class C ashfeedstock using hydrochloric acid in two stages starting withhydrochloric acid at pH 1.5 followed by 30% hydrochloric acid.

FIG. 30 is a table depicting leaching results of class C ash feedstockusing 30% hydrochloric acid for 24 hours on the residue after leachingin FIG. 29 .

FIG. 31 graphically depicts 11% versus 30% hydrochloric acid leachatesfor class C ash feedstock.

FIG. 32 graphically depicts 11% versus 30% hydrochloric acid leachatesfor class F ash feedstock.

FIG. 33 graphically depicts elemental composition of 11% versus 30%hydrochloric acid residues for class C ash and class F ash feedstocksfrom FIG. 28 and FIG. 29 leaches.

FIG. 34 depicts X-ray Diffraction (XRD) mineralogical compositions ofclass C and class F leach residues resulting from FIG. 28 and FIG. 29leaches.

FIG. 35 is a flowsheet depicting a two-stage leach embodiment.

FIG. 36 is a chart depicting the excellent separation and cumulativeelemental precipitation percent versus pulp pH for class C ash feedstockusing caustic.

FIG. 37 is a chart depicting the cumulative precipitation of rare earthelements (REE) versus pulp pH for class C ash feedstock using causticwith the bulk of the REEs precipitating between pH 4 and 8.

FIG. 38 is a table depicting the percent composition of the variousprecipitate hydroxides at different pHs using caustic for class C ashfeedstock.

FIG. 39 is a chart depicting percent elements precipitated at pH 3 forclass C ash feedstock with caustic.

FIG. 40 is a chart depicting percent elements precipitated at pH 4 forclass C ash feedstock with caustic.

FIG. 41 is a chart depicting percent elements precipitated at pH 5-8 forclass C ash feedstock with caustic.

FIG. 42 is a chart depicting percent elements precipitated at pH 5-8 forclass C ash feedstock with caustic and with aluminum removed to show thesmaller percentage more clearly.

FIG. 43 is a chart depicting percent elements precipitated at pH 9 forclass C ash feedstock with caustic.

FIG. 44 is a chart depicting percent elements precipitated at pH 10 forclass C ash feedstock with caustic.

FIG. 45 is a chart depicting percent elements precipitated at pH 2.5 forclass C ash feedstock with caustic.

FIG. 46 is a table depicting cations and anion for the sodium chloridefinal stream anions for class C ash feedstock after causticneutralization.

FIG. 47 is a chart depicting cumulative precipitations versus pH for thelime flowsheet (calcium carbonate and calcium hydroxide) for class C ashfeedstock.

FIG. 48 is a table showing results from the lime precipitation flowsheettesting.

FIG. 49 depicts an optional process embodiment for refining a silicaproduct by burning off carbon.

FIG. 50 depicts another optional process embodiment for refining asilica product by using caustic fusion.

FIG. 51 depicts the process for converting sulfite to sulfate.

FIG. 52 depicts the kinetic data for the conversion of sulfite tosulfate at 50% oxygen with Mn catalyst.

FIG. 53 depicts the kinetic data for the sulfite to sulfate reaction at10% oxygen with Mn catalyst.

FIG. 54 depicts the kinetic data for the sulfite to sulfate reactionwith just air and the Mn catalyst.

FIG. 55 depicts a phosphogypsum assay of a U.S. Sample.

FIG. 56 depicts semi-quantitative X-ray diffraction results.

FIG. 57 depicts a production process for phosphogypsum conversion.

FIG. 58 depicts a calcium carbonate whitening process for PG gypsumflowsheet.

FIG. 59 is a Scanning Electron Micrograph of the nanoparticle size ofour precipitated calcium carbonate particles.

FIG. 60 is a Scanning Electron Micrograph of the fibrous Mullite in thecoal ash residue.

FIG. 61 shows a standard method for producing phosphoric acid fromphosphate rock and producing phosphogypsum as a byproduct.

Elements and acts in the figures are illustrated for simplicity and havenot necessarily been rendered according to any particular sequence orembodiment.

DETAILED DESCRIPTION

Although the disclosure described herein is susceptible to variousmodifications and alternative iterations, specific embodiments thereofhave been described in greater detail herein. It should be understood,however, that the detailed description of the systems and methods is notintended to limit the disclosure to the specific embodiments disclosed.Rather, it should be understood that the disclosure is intended to covermodifications, equivalents, and alternatives falling within the spiritand scope of the disclosure. In the following description, and for thepurposes of explanation, numerous specific details, process durations,and/or specific formula values are set forth in order to provide athorough understanding of the various aspects of exemplary embodiments.However, it will be understood by those skilled in the relevant artsthat the apparatus, systems, and methods herein may be practiced withoutall of these specific details, process durations, and/or specificformula values. It should be noted that there are different andalternative configurations, devices, and technologies to which thedisclosed embodiments may be applied. The full scope of the embodimentsis not limited to the examples that are described below.

In the following examples of the illustrated embodiments, references aremade to the accompanying drawings which form a part hereof, and in whichis shown by way of illustration various embodiments in which thesystems, methods, processes, and/or apparatuses disclosed herein may bepracticed. It is to be understood that other embodiments may beutilized, and structural and functional changes may be made withoutdeparting from the scope.

Headings are for organizational purposes only and are not intended to belimiting. Embodiments described under the various headings herein areinteroperable with embodiments under other headings.

OVERVIEW

FIG. 1 depicts an ash conversion process 1800 combined with an FGDgypsum conversion process 200 (FIG. 2 ). The depicted ash conversionprocess 1800 may be the lime embodiment 1800 a (FIGS. 18 and 19 ) or thecaustic embodiment 1800 b (FIGS. 20 and 21 ) or variations thereof asdisclosed herein. In the depicted embodiment of the combined conversionsystem and method, FGD gypsum feedstock that is mixed with ash isprocessed in the FGD gypsum conversion process 200 resulting in anammonium sulfate product and a calcium carbonate product that is mixedwith ash. The calcium carbonate and the FGD are insoluble and areseparated in the filtration process. The calcium carbonate product thatis mixed with ash is processed through the ash conversion process 1800resulting in the ash conversion process products as disclosed herein. Inreference to the FIGS. 2, 18, and 20 , the calcium carbonate, mixed withash, from dryer 225 (FIG. 2 ) in the FGD gypsum conversion processproceeds to leach tank 1810 (FIGS. 18 and 20 ) in the ash conversionprocess.

Gypsum Conversion Systems and Methods

Disclosed herein are systems and methods for reacting flue gasdesulfurization (FGD) gypsum (calcium sulfate) feedstock orphosphogypsum (PG), in either batch or continuous mode, with an ammoniumcarbonate reagent to produce commercial products, wherein the commercialproducts comprise ammonium sulfate and calcium carbonate. The FGD gypsummay have impurities as shown in FIG. 3 . The systems and methodsdescribed herein are highly beneficial to the coal industry in that theyproduce higher value products from coal waste. The primary reaction isshown in equation (2) below.

CaSO₄.2H₂O (insoluble)+(NH₄)₂CO₃ (soluble)→(NH₄)₂SO₄ (soluble)+CaCO₃(insoluble)+2H₂O   (2)

The mixture of ammonium sulfate and calcium carbonate is referred to asthe first reacted slurry. FIG. 2 depicts an embodiment of a productionplant 200 for implementing an FGD gypsum conversion process resulting inat least two commercial products. In the depicted embodiment, FGD gypsum(calcium sulfate) feedstock is fed, either in batch or continuous mode,into a reactor cascade 205 (comprising reactors 210, 211, 212, and 213)with ammonium carbonate reagent, which may be synthesized from ammoniaand carbon dioxide gases or supplied as a powder. In some embodiments,the FGD gypsum feedstock may be fed to the system using a quantitativepowder feeder or a gravimetric feeder optionally coupled to a screwfeeder (not shown). In some embodiments, the FGD gypsum feedstock is inpowder form. In embodiments where the FGD gypsum feedstock is moist, itmay require drying prior to feeding to avoid blockages in the feeder. Insome embodiments, the FGD gypsum feedstock may be dried to 7% by weightor less moisture content.

The number of reactors in the reactor cascade 205 may vary depending onthroughput required, the size and type of reactors, and the reactiontime needed. In some embodiments, there may be between three and fivereactors. As an example, for a two-hour reaction with four reactorshaving total volume V, the scaled total volume needed would be 4/3 V forthree reactors and 2V for two reactors. The same rule applies whenincreasing the number of reactors. In some embodiments, the size of thereactors 210, 211, 212, and 213 may be reduced using weirs.

The one or more reactors 210, 211, 212, and 213 may be connected inoverflow mode (material overflows from the top of a reactor to the nextreactor) or underflow mode (material flows from the bottom of a reactorto the next reactor), or material may be transferred using one or morepumps between the one or more reactors. In some embodiments, the one ormore reactors 210, 211, 212, and 213 may be continuously stirred tankreactors (CSTRs), stirred tank reactors and/or plug-flow reactors. Insome embodiments, the first reactor 210 may be a small, high intensityreactor to thoroughly mix the FGD gypsum feedstock and reagent, followedby two to three (larger, in some embodiments) reactors 211, 212, and/or213 to hold the mixture long enough for the reaction to reach completion(i.e. 99+% conversion of FGD gypsum feedstock) resulting in a reactedslurry. In the depicted embodiment, the reactor cascade 205 ventsammonia gas from the ammonium carbonate reagent through vent 215 a tothe scrubber 217. Either water or between 0.01 to 0.1M sulfuric acid maybe used in the scrubber 217. The ammonia from the vents 215 a-edissolves in water to yield ammonium hydroxide or, in the case ofsulfuric acid, the ammonia reacts to form ammonium sulfate. The ammoniumhydroxide or ammonium sulfate from the scrubber 217 may optionally berecycled back into the reagent feed line into reactor 210, in someembodiments.

After the reaction has reached completion, the first reacted slurry ispumped, underflows, or overflows from the reactor cascade 205 into afilter 220 resulting in calcium carbonate residue and ammonium sulfatefiltrate. Wash water is pumped through filter 220 in the depictedembodiment. Ammonia off-gases from the filter 220 vent through vent 215c to scrubber 217. In some embodiments, filter 220 may be a drum filteror other similar continuous filter. The calcium carbonate residue fromfilter 220 proceeds to dryer 225 to produce calcium carbonate product.In the depicted embodiment, dryer 225 vents through vent 215 c ammoniato scrubber 217. In some embodiments, the calcium carbonate product maybe further processed. Further processing options are discussed in theExamples.

In the depicted embodiment, ammonium sulfate filtrate proceeds fromfilter 220 to evaporator 230 where water is evaporated from the ammoniumsulfate liquor to form an ammonium sulfate liquor, and then tocrystallizer 235 where ammonium sulfate crystals are produced in theammonium sulfate liquor. Centrifuge 240 separates the ammonium sulfatecrystals from the ammonium sulfate liquor resulting in separatedammonium sulfate crystals and saturated ammonium sulfate liquor. Dryer245 dries the separated ammonium sulfate crystals resulting in ammoniumsulfate product. The dryer 245 vents through vent 215 e to scrubber 217.In some embodiments, saturated ammonium sulfate liquor may be pumpedfrom the centrifuge 240 back into the evaporator 230. Overheads orvapors coming off the top of the evaporator 230, containing excessammonium carbonate reagent, may optionally proceed through a condenser250 (evaporator condensate) to be recycled back into the reactor cascade205 to react with the FGD gypsum feedstock thus reducing reagent demandand reducing waste streams. In the depicted embodiment, water is pumpedinto the reactor cascade 205 and into the ammonia scrubber 217. In thedepicted embodiment, all off-gases, including water vapor and ammonia insome embodiments, vent through vents 215 a, 215 b, 215 c, 215 d, 215 eto ammonia scrubber 217.

In some embodiments, the ammonium sulfate may be vacuum evaporated toform a salt. The salt may then be allowed to crystallize out, and thecrystallized product is then filtered using a solid/liquid separationdevice. The conditions in the crystallizer 235 may be controlled toproduce larger crystals which are more desirable in some markets. Theammonium sulfate product may be greater than or equal to 99% pure. Theammonium sulfate crystallization and the centrifuge separation processesmay be continuous or batch processes.

Filter 220 and centrifuge 235 are both solid/liquid separators and maybe substituted by other solid/liquid separators in other embodiments.For example, a belt filter may be used in place of filter 220 and arotating drum filter may be used in place of the centrifuge 235. In someembodiments, a spray dryer may be used in place of the evaporator 230and crystallizer 235. The spray dryer evaporates the water and formssmall crystals all in one step. Continuous filtration systems other thanthose depicted in FIG. 2 may be utilized in the process. The equipmentused in the process may be sized to fit the desired input/output.Material transfer between processes and/or equipment may be carried outwith the use of pumps, etc.

Reagents

In the embodiment depicted in FIG. 2 , ammonium carbonate reagent issynthesized using ammonia (NH₃) and carbon dioxide (CO₂) gases inflowing water. In some embodiments, the NH₃ and CO₂ gas are injected inthe stoichiometric ratio of 2:1 respectively. The gases may beintroduced sequentially using gas nozzles into a flowing water stream ineither a batch process or a continuous process. The gases are best fedsequentially with the NH₃ first followed by the CO₂ because NH₃ is moresoluble in water than CO₂ and CO₂ is more soluble in ammonium hydroxidethan in plain water. This order of gas introduction into the water hasbeen found to reduce the chances of an ammonia gas release. Inalternative embodiments, the order of gas introduction into the watermay be reversed. Sequential feed of the NH₃ and CO₂ gases reduces chanceof clogging in the gas nozzle; however, the NH₃ and CO₂ gases may bepremixed, in some embodiments. The NH₃ and CO₂ gases may be mixed withprocess water using a mixer 108 such as an in-line mixer or a reactortank with mixer resulting in an ammonium carbonate reagent solution. Insome embodiments, the gases may be fed directly into mixer 208.

The pH may optionally be monitored to ensure carbonate is formed (formedbetween pH 8.7-9.0), rather than bicarbonate, which is formed at lowerpHs. Conductivity and/or the specific gravity may be monitored using anelectric conductivity meter and a hydrometer, respectively, to determinethe concentration of ammonium carbonate reagent formed. Bothconductivity and specific gravity increase as the concentration of theammonium carbonate formed in solution increases. For example, for a 15%concentration of ammonium carbonate in solution, the conductivity is80-90 mS/cm (milli-siemens/centimeter).

The resulting ammonium carbonate reagent may be fed directly intoreactor cascade 205. In some embodiments, the ammonium carbonate reagentis added in excess (more than stoichiometric) to ensure the reactiongoes to completion (i.e. until all the FGD gypsum feedstock is reacted).In some embodiments, 140% stoichiometric addition of the ammoniumcarbonate reagent results in the reaction going to completion. If thereaction is not complete, then the calcium carbonate product iscontaminated with FGD gypsum feedstock.

Products

In some embodiments, to make the products more commercially attractive,the ammonium may be agglomerated in an agglomerator to larger, moreflowable particles to facilitate product application. In someembodiments, the particles are several millimeters in size. In someembodiments the ammonium sulfate and/or calcium carbonate products maybe further treated with coating agents, such as stearic acid andstearates, to improve their properties for specific markets, such as toreduce their moisture absorption. In some embodiments, the ammoniumsulfate and/or calcium carbonate products may be treated with anadditive to reduce the absorption of water.

Ammonium Sulfate

The ammonium sulfate product produced by production plant 200 (FIG. 2 )may be used as a solution. In some embodiments, the ammonium sulfateproduct is greater than 99% pure. In some embodiments, the ammoniumsulfate solid product is fertilizer grade. Ammonium sulfate is primarilyused in the global fertilizer industry as a soil amendment to replenishdepleted levels of nitrogen and sulfur to the soil. An additional use inthe fertilizer industry is as an adjuvant for various insecticides,herbicides, and fungicides. Ammonium sulfate may also be used innon-agricultural products and processes such as for flameproofing ofselect materials, textile dyeing, a cattle feed supplement, and forcertain water treatment processes.

Calcium Carbonate

The calcium carbonate product produced by production plant 200 (FIG. 2 )is insoluble. In some embodiments, the calcium carbonate product maycontain small amounts of impurities, such as carbon and iron, which maycause it to have a grey or tan color. In the case of phosphogypsum,these impurities also contain valuable rare earth elements (REEs) aswell thorium and uranium (FIG. 56 ). In some embodiments, the calciumcarbonate is 90-99 wt % pure. In some embodiments, the calcium carbonateproduct may be further processed to obtain a higher purity whiteprecipitated calcium carbonate (PCC) product which typically has highermarket value. Some exemplary calcium carbonate whitening processes aredescribed in the examples under the heading Calcium Carbonate Processingbelow (FIGS. 15, 17, 58 ).

Calcium carbonate has a plethora of uses in many diverse industriesincluding: the oil and gas industry as drilling fluid make-up toincrease the fluid density, as an additive to control fluid loss toformation, and in oilfield cementing as a loss circulation material; thebuilding materials and construction industry for roofing shingles,tiles, and cement, brick, and concrete block manufacture; and commercialapplications such as industrial filler in the paper, paint, plastics,and rubber industries.

Calcium Carbonate Processing 1. Acid Dissolution

In some embodiments, the calcium carbonate product produced by the FGDgypsum conversion process may comprise contaminants such as iron,carbon, and silicates. When such contaminants are present, the calciumcarbonate may proceed through further processing to remove suchcontaminants resulting in a purer product. In some embodiments, such asthe acid dissolution calcium whitening system and process 1500 depictedin FIG. 15 , the calcium carbonate product may be dissolved in dissolver1502 in dilute acid (such as hydrochloric acid (HCl), nitric acid(HNO₃), or another acid forming a soluble calcium salt). The basicreaction is shown in equation (3) below:

CaCO₃ (insoluble)+2HCl+impurities→CO₂+Ca(Cl)₂ (soluble)+H₂O+impurities  (3)

The carbon dioxide generated by equation 2 in dissolver 1502, in thedepicted embodiment, may proceed to scrubber 1505 containing sodiumhydroxide to form sodium carbonate or optionally potassium hydroxide toform potassium carbonate or ammonium hydroxide to produce ammoniumcarbonate.

The mixture resulting from equation 3 may then be filtered by filter1510 with solid impurities proceeding to dryer 1515 and liquidsproceeding to reactor 1520. The dried solids may comprise carbon andsilicates, in some embodiments. If an iron contaminant is present in thecalcium carbonate product produced by the FGD conversion process,hydrogen peroxide (H₂O₂) may be added to reactor 1520 to oxidize ferrousiron to ferric iron. An amount of base such as calcium hydroxide (indepicted embodiment), sodium hydroxide, and/or sodium carbonate may alsobe added to reactor 1520 to raise the pH in the reactor to 3 or higherto precipitate ferric hydroxide. The advantage of using calciumhydroxide is that the amount of high purity precipitated calciumcarbonate produced is increased by the amount of calcium neutralizingagent used, thus improving process economics. The amount of base addedis the amount that is necessary to reach the desired pH value. Thisreaction with sodium hydroxide and hydrogen peroxide is shown inequation (4), below:

Fe⁺⁺+H₂O₂+NaOH→Fe(III)(OH)₃ (insoluble)+Na⁺  (4)

The slurry resulting from equation 4 in reactor 1520 may be filteredwith filter 1525 to remove ferric hydroxide solids. In some embodiments,some carbon impurity may also filter out with the ferric hydroxide. Insome embodiments, the ferric hydroxide is transferred to calciner 1530resulting in a ferric oxide product.

In some embodiments, one or more pH adjustments and filtration steps toprecipitate and filter other impurities (FIG. 3 ) may be performed inaddition to those described here. FIG. 38 shows compositions of metalsthat can be precipitated at different pH levels. Precipitation ofdifferent metals is further described below.

The filtrate from filter 1525 comprises a purified calcium chloridesolution, or a mixed calcium and sodium chloride solution depending onthe base used, which may then be combined with sodium carbonate, carbondioxide, potassium carbonate, ammonium carbonate, or another solublecarbonate in reactor 1535 to produce precipitated calcium carbonate. Themixture may proceed through filter 1540 to separate solids and liquids.The solids may proceed through dryer 1545 to produce a white and highpurity (>98%) precipitated calcium carbonate product. The precipitationreaction with sodium carbonate is shown in equation (5).

Ca(Cl)₂+Na₂CO₃→2NaCl+CaCO₃(insoluble)   (5)

The precipitated calcium carbonate (PCC) is high purity and is anagglomeration of nano particles (FIG. 59 ) which increases its highvalue applications.

The filtrate from filter 1540 may proceed through dryer 1555 to producesodium chloride. If potassium carbonate is used instead of sodiumcarbonate, the product would be potassium chloride, which can be used asa fertilizer. If ammonium carbonate is used instead of sodium carbonate,the product would be ammonium chloride, which can also be used as afertilizer.

In some embodiments wherein HCl was used in the acid dissolution calciumcarbonate whitening process, the economics of the purification ofcalcium carbonate may be significantly improved if the resultant NaClfiltrate is regenerated back to NaOH and HCl using a chlor-alkali cellprocess.

In some embodiments wherein HNO₃ is used in the acid dissolution, theproducts produced would be sodium nitrate, potassium nitrate, andammonium nitrate depending on the soluble carbonate used, each of whichis a fertilizer. They each also produce precipitated calcium carbonate.In some embodiments wherein phosphoric acid is used in the aciddissolution, the products produced would be converted to sodiumphosphate, potassium phosphate, or ammonium phosphate. They all alsoproduce precipitated calcium carbonate.

In the case of the calcium carbonate produced from a phosphogypsumfeedstock, an acid such as nitric acid, hydrochloric acid, or any otheracid forming a soluble calcium salt, is used to dissolve the calciumcarbonate. The CO₂ generated from that reaction is absorbed in a basesuch as ammonium hydroxide or sodium hydroxide to form the correspondingcarbonates. There are then two approaches to separate the REEs and theradioactive elements as well as the other impurities: The first approachis to adjust the final pH in the initial dissolution to different valuessuch that different impurities can be separated. The second approach isto dissolve all the impurities under acid conditions and then separatethem by incremental increases in pH (FIG. 59 depicts the process andthese options). This second approach is based on the separationtechnology disclosed in the “Ash Conversion Systems and Methods”. Thefinal processing step is to use the ammonium carbonate (or sodiumcarbonate) produced to precipitate the solubilized calcium to form ahigh purity, nano-sized (SEM in FIG. 60 ) precipitated calcium carbonate(PCC). FIG. 16 depicts a whitened calcium carbonate product generated bythe calcium whitening process depicted in FIG. 15 . 2. Catalyst

In some embodiments, a catalyst to delay the formation of calciumcarbonate may be added to the reactor cascade 205 (FIG. 2 ) so thatimpurities (or impurities plus ash, in some embodiments) may be filteredout before the precipitate is formed. The addition of a catalyst resultsin a fine white and high purity (>98%) precipitated calcium carbonateproduct.

FGD gypsum feedstock may comprise contaminants including carbon and/orfly ash, in some embodiments. An example embodiment of a process forusing a catalyst to separate impurities from calcium carbonate isdepicted in FIG. 17 . In some embodiments, a quantity of a catalyst(0.5-7% by weight, in some embodiments) may be added to an FGD gypsumslurry mixture in a reactor 1710 wherein the FGD gypsum slurry mixturecomprises a suspension in the range of 1% to 25% (4%, in someembodiments) weight by mass of FGD gypsum feedstock in water. Thecatalyst is allowed to mix, by means of a stirring mechanism in someembodiments, with the slurry for several minutes (5-30 minutes, in someembodiments). After mixing, an ammonium hydroxide solution may be addedto the reactor vessel 1710 resulting in 1:1 ammonium hydroxide to slurryvolumetric ratio. This addition of the ammonium hydroxide is immediatelyfollowed by the introduction of carbon dioxide gas at a rate of 4L/minute±1 L/minute, in some embodiments. The concentration of theammonium hydroxide solution is the concentration required tostoichiometrically react with all of the sulfate in the FGD gypsumslurry to form ammonium sulfate according to equation (6):

2NH₄OH+CaSO₄.2H₂O+CO₂→(NH₄)₂SO₄+CaCO₃+3H₂O   (6)

The progress of the reaction can be followed by monitoring the pH whichstarts out at approximately 11.6 and with time drops to pH 7. At pH 7all hydroxide has reacted and the solution is filtered (immediately, insome embodiments) through a 0.45 to 0.7 micron filter 1730. Filtrationof the reacted FGD gypsum solution results in the separation of trampfly ash and carbon from the resulting liquid comprising dissolvedcalcium carbonate and ammonium sulfate. The calcium carbonate insolution will separate from the ammonium sulfate solution in delayholding tank 1735 and can be collected by an additional filtration step1740 using a 0.45 to 0.7 micron filter. In some embodiments, one or moreof the filtration steps may be carried out using a filter composed ofglass fibers.

The precipitation of calcium carbonate may be aided by seeding thesolution with the desired crystalline form of calcium carbonate. In someembodiments, a small amount of precipitated calcium carbonate may berecycled back to the reactor cascade 205 (FIG. 2 ). The seeds may becalcite. In some embodiments, the precipitated calcium carbonateparticles may be nanoparticles. In some embodiments, the solutioncontaining the calcium carbonate may be heated to cause the calciumcarbonate precipitate to coagulate, thus improving filtration. Thesolution passing filtration step 1740 contains the ammonium sulfatewhich can be harvested by various crystallization methods known in theart. In some embodiments, a catalyst is used to slow down theprecipitation of calcium carbonate in order to allow the solution to befiltered. Some of the catalyst may remain in the ammonium sulfatesolution and/or the crystallized product. The catalyst does not reactwith the reactants therefore it may be recaptured and/or recycled, insome embodiments.

In some embodiments, the filtered ammonium sulfate solution may bereturned to the beginning of the process to make up the FGD gypsumfeedstock slurry. In some embodiments, the appropriate concentration ofcatalyst may remain in the recycled solution such that no furtheraddition of the catalyst is necessary. In some embodiments, morecatalyst may be added to the solution as needed.

The calcium carbonate whitening process with catalyst can also beperformed in the production plant embodiment shown in FIG. 2 with somemodifications. For instance, referring to FIG. 2 , the calcium carbonatewhitening process with catalyst of FIG. 17 may replace filter 220.Reacted slurry from the reactor cascade 205 would proceed into reactor1710 (FIG. 17 ) through the process depicted in FIG. 17 with the liquorfrom filter 1740 (FIG. 17 ) proceeding to evaporator 230 and thewhitened calcium carbonate optionally proceeding through dryer 225. Insome embodiments, the catalyst may be added to the reactor cascadedirectly and the reacted slurry with catalyst may proceed from thereactor cascade 205 to filter 1730 (FIG. 17 ) (i.e. reactor cascade 205from FIG. 2 replaces reactor 1710 in FIG. 17 ).

Environmental Benefits

The processes described herein are environmentally sound with internalrecycles and near zero waste. All parts of the processes where ammoniagas may be released may be exhausted to one or more water (or dilutesulfuric acid) scrubbers where the ammonia is recaptured and recycled toone or more of systems/processes (FIGS. 2 & 58 ). Coupling to anadjacent Haber process (a process for producing ammonia from nitrogenand hydrogen), in some embodiments, could minimize the amount of ammoniathat would need to be stored on site, thus reducing the hazardsassociated with storing large quantities of ammonia. Locating aproduction plant 200 (FIG. 2 ) near a source of carbon dioxide, such asa coal power plant in some embodiments, could allow around 10% by volumeof the carbon dioxide emissions from the coal power plant to be utilizedin the production plant 200 (FIG. 2 ) using a side stream taken from theexhaust stack. CO₂ gas may be provided from other processes, plants, orsources including naturally occurring or stored CO₂ gas which may bepumped from underground formations. Carbon capture is another potentialenvironmental benefit of the processes described herein as CO₂ gas isconverted to a solid carbonate compound. In some embodiments, one ormore internal recycles may be incorporated to recover reagents resultingin near-zero waste streams, which is of significant environmentalbenefit.

FGD Gypsum Feedstock Mixed with Ash

In some embodiments, where the FGD gypsum feedstock is mixed with coalash, the FGD conversion process can produce a high purity ammoniumsulfate and a second product that is comprised of calcium carbonate andash (FIG. 1 ). This product can be marketed as such, particularly tobuilding material applications, or further processed in other separationschemes. The processing system and methods for FGD gypsum feedstock thatis mixed with ash is the same as that depicted in FIG. 2 ; however, thecalcium carbonate product may be lower purity than that generated froman FGD gypsum feedstock that is not mixed with ash. The amount of ash inFGD gypsum feedstock that is mixed with ash affects the purity of thecalcium carbonate product when FGD gypsum feedstock mixed with ash isused in the FGD gypsum conversion process. FIG. 1 depicts a processwhere FGD feedstock mixed with ash can be processed in the FGDconversion process and the calcium carbonate mixed with ash can beprocessed in the ash conversion process depicted in FIGS. 18 through 21. In some embodiments, where the FGD sulfite feedstock is mixed withcoal ash, The sulfite is first converted to sulfate via oxidationdescribed in the next section and then processed through the FGDconversion to produce a high purity ammonium sulfate and a secondproduct that is comprised of calcium carbonate and ash.

Removal of Chloride from Flue Gas Desulfurization Gypsum Feedstock

Some FGD gypsum feedstock contains levels of chloride that are too highfor certain applications. The excess chloride is removed from FGD gypsumfeedstock through a process of water leaching, in some embodiments.Water leaching may be carried out at any temperature between roomtemperature (20° C.) and boiling (100° C.).

There are several techniques to remove impurities from the filtrateafter the water leach before discharge including ion exchange columns,reverse osmosis, and other similar deionization techniques known in theart.

A test was run to determine where the chloride in FGD gypsum feedstockwinds up when processed through the FGD gypsum conversion process. Inthe test, FGD gypsum feedstock containing 0.5% by weight chloride wasprocessed by reacting with ammonium carbonate to convert the calciumsulfate to calcium carbonate and ammonium sulfate. That test showed thatthe CaCO₃ product had a chloride concentration of 16 ppm and theammonium sulfate had a chloride concentration of 434 ppm. The filtratefrom the ammonium sulfate crystallization had a chloride concentrationof 672 ppm. On a weight percentage basis, the filtrate from the ammoniumsulfate crystallization contains most of the chloride at 94.2% byweight, the ammonium sulfate contained 5.2% by weight, and the calciumcarbonate 0.6% by weight. These results showed that water leaching toremove chlorides in the FGD gypsum feedstock prior to FGD conversionprocessing greatly enhances the purity of the ammonium sulfate andcalcium carbonate products by reducing the chloride impurity from 0.5%by weight to 100 ppm.

Sulfite to Sulfate Conversion

In some cases, the FGD gypsum feedstock may be in the form of a calciumsulfite slurry. In such embodiments, an oxidation step may be requiredto convert calcium sulfite to calcium sulfate. While there are severalwell-established methods to oxidize calcium sulfite to calcium sulfate,none have been coupled to a more comprehensive conversion process. Theconversion of calcium sulfite to calcium sulfate (gypsum) in thescrubber tower with air is known in the art. There are a number ofoxidation methods that may be coupled to the FGD conversion processdepicted in FIG. 2 . FIG. 14 depicts a modified production plant 200(FIG. 2 ) with the addition of an oxidation step 1400 for calciumsulfite to calcium sulfate conversion prior to feeding into the FGDgypsum conversion process.

Forced Air Oxidation: Conventional sparger oxidation bubble towers,which are expensive to build, can measure up to 60 feet in height andrequire 200% excess air to achieve complete conversion of calciumsulfite to calcium sulfate. A newer and less expensive approach uses airturbine oxidizer systems. These could be sited remotely and greatlyreduce the conventional air oxidation retrofit. This process is alsoaccomplished in an acidic environment. The calcium sulfite is extremelysoluble in an acid medium and the sulfite ion in solution oxidizes veryquickly in an agitated solution to a sulfate ion. Once the calciumsulfate forms, it precipitates to a gypsum slurry very rapidly. Otherapproaches use mechanical agitation for froth flotation with added airoxidation.

Air Oxidation over Time: Calcium sulfite will eventually convert tocalcium sulfate when exposed to air and in the presence of water or in aslurry. The reaction is very slow and does not meet normal processrequirements. However, inventories that have been stored outdoors for along period of time may have mostly converted to calcium sulfate and canbe used directly in the FGD gypsum conversion processes describedherein. The mere fact that calcium sulfite is recognized as a mineralsuggests that the sulfite to sulfate conversion kinetics are extremelyslow.

Hydrogen Peroxide Oxidation: Sulfur dioxide, and/or its aqueousbyproduct sulfite, may be oxidized to sulfate with hydrogen peroxide.The reaction occurs over a wide pH range but is faster at lower pHs.This is conducted in an aqueous medium and involves the oxidation ofdissolved sulfite ion with peroxide to convert to the more insolublesulfate. Calcium peroxide may be used in place of hydrogen peroxide.

Oxidation with Oxygen: The oxidation of calcium sulfite to calciumsulfate may be accelerated by using oxygen in place of air. The reactionmay be performed at a low pH such as 4-5 to facilitate the reaction. Inanother embodiment, a low concentration of a metal ion is added as acatalyst aid in the reaction. Examples of suitable catalysts include 5to 10 ppm ferric ion, manganese (II), or cobalt (II). The oxygenoxidation and catalyst process to convert sulfite to sulfate describedin this disclosure may be performed in either a batch or in a continuousprocess. The primary reactions using a manganese catalyst are shown inequations (7) and (8) below.

2CaSO₃+O₂+Mn⁺⁺ (catalyst)→2CaSO₄+Mn⁺⁺ (catalyst)   (7)

CaSO₄.2H₂O (insoluble)+(NH₄)₂CO₃ (soluble)→(NH₄)₂SO₄ (soluble)+CaCO₃(insoluble)+2H₂O   (8)

FIG. 51 depicts an embodiment of a process for converting calciumsulfite to calcium sulfate.

FIG. 14 depicts an embodiment of a process to convert calcium sulfite tocalcium sulfate and then converting it to ammonium sulfate and calciumcarbonate with ammonium carbonate.

The systems and methods disclosed herein were first developed by testingbatch reactions under different conditions to oxidize sulfite to sulfateand arrive at initial operating conditions for a continuousdemonstration. Initial test at pHs of 8-9 using an iron catalyst werenot successful. Tests were run using 50% oxygen and 10% oxygen. However,a small reaction was observed at 50% oxygen at pH of 8. This indicatesthat lower pHs are more desirable.

Systems and methods are disclosed herein for continuous oxidation ofcalcium sulfite to calcium sulfate using an oxidizing gas stream of 50%or more of oxygen mixed with air to sparge through the sulfite slurryfeedstock to form calcium sulfate. The pH of the sulfite slurry may belowered from about 6.8 to between about 4-5 which may be maintainedthroughout the reaction. Concentrated sulfuric acid such as 20 wt % maybe used to maintain the pH and keep all anions as sulfates. In someembodiments after dosing the sludge mix with oxygen, sulfuric acid maybe added to maintain the low pH necessary for the reaction to takeplace. Below pH 4, SO₂ is evolved; above pH 5, the reaction is sloweddown. A catalyst of manganous ion with a concentration of 1-10millimolar (mmol) may be used to accelerate the reaction. Othercatalysts such as iron and cobalt (II) may also be used. The reactionmay carried out at ambient temperature, as higher temperatures reducethe oxygen solubility in water.

In an example of this embodiment, the reaction was >95% complete afterabout 4 hours of sparging with 50% oxygen and 3.2 mmol of Mn ion. When10% oxygen and 3.2 mmol Mn was used, the reaction was less effective andresulted in only 32% conversion after 6 hours. With air in place ofoxygen, the conversion was only 20-30% after six hours. Two differenttechniques were used to measure the conversion: 1) X-ray diffraction(QXRD), and 2) Thermogravimetric analysis (TGA). FIGS. 52, 53 and 54show the conversion % as a function of time under 50% oxygen, 10%oxygen, and air conditions, respectively.

Phosphogypsum Conversion Systems and Methods Summary

Phosphogypsum can be processed to produce ammonium sulfate crystals,precipitated calcium carbonate, REE misch metals, thorium and uranium,and ammonium nitrate solution. Phosphogypsum is a byproduct of theproduction of phosphoric acid from phosphate rock using sulfuric acid(FIG. 61 ). Process flowsheets developed for an example phosphogypsumprocess are shown in FIGS. 57 and 58 . The process may be a batchprocess or a continuous process.

Disclosed herein are systems and methods for reacting phosphogypsum(PG), in either batch or continuous mode, with an ammonium carbonatereagent to produce commercial products, wherein the commercial productscomprise ammonium sulfate and calcium carbonate. The PG may haveimpurities as shown in FIG. 3 . The systems and methods described hereinare highly beneficial to the coal industry in that they produce highervalue products from coal waste. The primary reaction is shown inequation (9) below.

CaSO₄.2H₂O (insoluble)+(NH₄)₂CO₃ (soluble)→(NH₄)₂SO₄ (soluble)+CaCO₃(insoluble)+2H₂O   (9)

The mixture of ammonium sulfate and calcium carbonate is referred to asthe first reacted slurry. FIG. 57 depicts an embodiment of a productionplant 5700 for implementing a PG conversion process resulting in atleast two commercial products. In the depicted embodiment, PG (calciumsulfate) feedstock is fed, either in batch or continuous mode, into oneor more reactors 5705 (comprising reactors 5710, 5711, 5712, and 5713)with ammonium carbonate reagent, which may be synthesized from ammoniaand carbon dioxide gases or supplied as a powder. In some embodiments,the PG gypsum feedstock may be fed to the system using a quantitativepowder feeder or a gravimetric feeder optionally coupled to a screwfeeder (not shown). In some embodiments, the PG gypsum feedstock is inpowder form. In embodiments where the PG gypsum feedstock is moist, itmay require drying prior to feeding to avoid blockages in the feeder. Insome embodiments, the PG gypsum feedstock may be dried to 7% by weightor less moisture content.

The number of reactors 5705 may vary depending on throughput required,the size and type of reactors, and the reaction time needed. In someembodiments, there may be between three and five reactors. As anexample, for a two-hour reaction with four reactors having total volumeV, the scaled total volume needed would be 4/3 V for three reactors and2V for two reactors. The same rule applies when increasing the number ofreactors. In some embodiments, the size of the reactors 5710, 5711,5712, and 5713 may be reduced using weirs.

The one or more reactors 5710, 5711, 5712, and 5713 may be connected inoverflow mode (material overflows from the top of a reactor to the nextreactor) or underflow mode (material flows from the bottom of a reactorto the next reactor), or material may be transferred using one or morepumps between the one or more reactors. In some embodiments, the one ormore reactors 5710, 5711, 5712, and 5713 may be continuously stirredtank reactors (CSTRs), stirred tank reactors and/or plug-flow reactors.In some embodiments, the first reactor 5710 may be a small, highintensity reactor to thoroughly mix the PG gypsum feedstock and reagent,followed by two to three (larger, in some embodiments) reactors 5711,5712, and/or 5713 to hold the mixture long enough for the reaction toreach completion (i.e. 99+% conversion of PG gypsum feedstock) resultingin a reacted slurry. In the depicted embodiment, the reactor cascade5705 vents ammonia gas from the ammonium carbonate reagent through vent5715 a to the scrubber 5717. Either water or between 0.01 to 0.1Msulfuric acid may be used in the scrubber 5717. The ammonia from thevents 5715 a-e dissolves in water to yield ammonium hydroxide or, in thecase of sulfuric acid, the ammonia reacts to form ammonium sulfate. Theammonium hydroxide or ammonium sulfate from the scrubber 5717 mayoptionally be recycled back into the reagent feed line into reactor5710, in some embodiments.

After the reaction has reached completion, the first reacted slurry ispumped, underflows, or overflows from the reactor cascade 5705 into afilter 5720 resulting in calcium carbonate residue and ammonium sulfatefiltrate. Wash water is pumped through filter 5720 in the depictedembodiment. Ammonia off-gases from the filter 5720 vent through vent5715 c to scrubber 5717. In some embodiments, filter 5720 may be a drumfilter or other similar continuous filter. The calcium carbonate residuefrom filter 5720 proceeds to dryer 5725 to produce calcium carbonateproduct. In the depicted embodiment, dryer 5725 vents through vent 5715c ammonia to scrubber 5717. In some embodiments, the calcium carbonateproduct may be further processed. Further processing options arediscussed in the Examples.

In the depicted embodiment, ammonium sulfate filtrate proceeds fromfilter 5720 to evaporator 5730 where water is evaporated from theammonium sulfate liquor to form an ammonium sulfate liquor, and then tocrystallizer 5735 where ammonium sulfate crystals are produced in theammonium sulfate liquor. Centrifuge 5740 separates the ammonium sulfatecrystals from the ammonium sulfate liquor resulting in separatedammonium sulfate crystals and saturated ammonium sulfate liquor. Dryer5745 dries the separated ammonium sulfate crystals resulting in ammoniumsulfate product. The dryer 5745 vents through vent 5715 e to scrubber5717. In some embodiments, saturated ammonium sulfate liquor may bepumped from the centrifuge 5740 back into the evaporator 5730. Overheadsor vapors coming off the top of the evaporator 5730, containing excessammonium carbonate reagent, may optionally proceed through a condenser5750 (evaporator condensate) to be recycled back into the reactorcascade 5705 to react with the PG gypsum feedstock thus reducing reagentdemand and reducing waste streams. In the depicted embodiment, water ispumped into the reactor cascade 5705 and into the ammonia scrubber 5717.In the depicted embodiment, all off-gases, including water vapor andammonia in some embodiments, vent through vents 5715 a, 5715 b, 5715 c,5715 d, 5715 e to ammonia scrubber 5717.

In some embodiments, the ammonium sulfate may be vacuum evaporated toform a salt. The salt may then be allowed to crystallize out, and thecrystallized product is then filtered using a solid/liquid separationdevice. The conditions in the crystallizer 5735 may be controlled toproduce larger crystals which are more desirable in some markets. Theammonium sulfate product may be greater than or equal to 99% pure. Theammonium sulfate crystallization and the centrifuge separation processesmay be continuous or batch processes.

Filter 5720 and centrifuge 5735 are both solid/liquid separators and maybe substituted by other solid/liquid separators in other embodiments.For example, a belt filter may be used in place of filter 5720 and arotating drum filter may be used in place of the centrifuge 5735. Insome embodiments, a spray dryer may be used in place of the evaporator5730 and crystallizer 5735. The spray dryer evaporates the water andforms small crystals all in one step. Continuous filtration systemsother than those depicted in FIG. 57 may be utilized in the process. Theequipment used in the process may be sized to fit the desiredinput/output. Material transfer between processes and/or equipment maybe carried out with the use of pumps, etc.

Reagents

In the embodiment depicted in FIG. 57 , ammonium carbonate reagent issynthesized using ammonia (NH₃) and carbon dioxide (CO₂) gases inflowing water. In some embodiments, the NH₃ and CO₂ gas are injected inthe stoichiometric ratio of 2:1 respectively. The gases may beintroduced sequentially using gas nozzles into a flowing water stream ineither a batch process or a continuous process. The gases are best fedsequentially with the NH₃ first followed by the CO₂ because NH₃ is moresoluble in water than CO₂ and CO₂ is more soluble in ammonium hydroxidethan in plain water. This order of gas introduction into the water hasbeen found to reduce the chances of an ammonia gas release. Inalternative embodiments, the order of gas introduction into the watermay be reversed. Sequential feed of the NH₃ and CO₂ gases reduces chanceof clogging in the gas nozzle; however, the NH₃ and CO₂ gases may bepremixed, in some embodiments. The NH₃ and CO₂ gases may be mixed withprocess water using a mixer such as an in-line mixer or a reactor tankwith mixer resulting in an ammonium carbonate reagent solution. In someembodiments, the gases may be fed directly into the mixer.

The pH may optionally be monitored to ensure carbonate is formed (formedbetween pH 8.7-9.0), rather than bicarbonate, which is formed at lowerpHs. Conductivity and/or the specific gravity may be monitored using anelectric conductivity meter and a hydrometer, respectively, to determinethe concentration of ammonium carbonate reagent formed. Bothconductivity and specific gravity increase as the concentration of theammonium carbonate formed in solution increases. For example, for a 15%concentration of ammonium carbonate in solution, the conductivity is80-90 mS/cm (milli-siemens/centimeter).

The resulting ammonium carbonate reagent may be fed directly intoreactor cascade 5705. In some embodiments, the ammonium carbonatereagent is added in excess (more than stoichiometric) to ensure thereaction goes to completion (i.e. until all the PG feedstock isreacted). In some embodiments, 140% stoichiometric addition of theammonium carbonate reagent results in the reaction going to completion.If the reaction is not complete, then the calcium carbonate product iscontaminated with phosphogypsum feedstock.

Calcium Carbonate Whitening

FIG. 58 shows a process for producing a highly pure calcium carbonateproduct. The calcium carbonate may be purified by dissolution in asolvent 5802, such as a nitric acid solution in a dissolver 250. Thisdissolves the calcium but leaves most of the impurities (REEs,radioactive elements, and other impurities) undissolved, as shown inequation (10).

CaCO₃(s)+impurities (s)+2HNO₃→Ca(NO₃)₂ (l)+impurities (s)+CO₂ (g)+H₂O(g)   (10)

The carbon dioxide produced in this reaction may be vented to anammonium hydroxide scrubber 5810 to produce ammonium carbonate, as shownin equation (11):

CO₂ (g)+2NH₄OH (l)→(NH₄)₂CO₃ (l)+H₂O (l)   (11)

Highly acidic pHs may dissolve most of the impurities except silicatesand carbon. The insoluble silicates, carbon, aluminum silicates,mullite, and other impurities may be filtered 5814 before the slurryproceeds to a third reactor 5818. Although FIG. 58 depicts a singlereactor, in some embodiments, one, two, or three reactors may be used.Additionally, each reactor may perform one or more pH adjustments. Abase 5816, such as calcium hydroxide, sodium hydroxide, potassiumhydroxide, ammonium hydroxide, and other bases known in the art may beused to increase the pH. The pH can then be increased stepwise inreactor 260 to, for example, pH 4 to precipitate dissolved aluminum,iron, thorium and uranium as shown in FIGS. 47 and 48 . Next, the pH maybe raised to 9 using a base to precipitate dissolved manganese,lanthanum, praseodymium, cerium, neodymium, and yttrium as shown inFIGS. 47 and 48 . Then, the pH may be increased to 11 to precipitateREEs, Mg, and any other dissolved elements except calcium as shown inFIGS. 47 and 48 . Each of these pH adjustments may be performed in asingle reactor or in a plurality of reactors.

The insoluble impurities at the different pHs may be filtered 5820.Although FIG. 58 shows only one filter, some embodiments may have morethan one filter. In some aspects, the number of filters 5820 may beequal to the number of reactors 5818, and the slurry from each reactormay be filtered before proceeding to the next reactor. In some examples,there may be one, two, or three filters to filter the slurries from one,two, or three reactors, respectively.

The filtrate from each of the filters 5820 may proceed to a dryer 5822.Although FIG. 58 depicts only one dryer, in some embodiments there maybe more than one dryer. In some aspects, the number of dryers may beequal to the number of filters. In some examples, there may be one, two,or three dryers to filter the filtrates from one, two, or three filters.

After all pH adjustments have been performed and the reacted slurryfiltered, a calcium nitrate liquor remains. The calcium nitrate liquormay then be precipitated in a reactor 5826 by adding a soluble carbonate5828, such as ammonium carbonate, carbon dioxide, sodium carbonate, orpotassium carbonate. The result is a high purity precipitated calciumcarbonate (PCC) and, when ammonium carbonate is used, a solution ofammonium nitrate, which may be marketed as a fertilizer. The reaction ofammonium carbonate and calcium nitrate is shown in equation (12):

Ca(NO₃)₂ (l)+(NH₄)₂CO₃ (l)→CaCO₃ (s)+2NH₄NO₃ (l)   (12)

To maintain the process as a net carbon capture, the carbon dioxideevolved during the dissolution of the calcium carbonate is absorbed inan ammonium hydroxide scrubber and then used as the reagent toprecipitate the PCC product, as shown in equation (13):

CO₂ (g)+2NH₄OH (l)→(NH₄)₂CO₃ (l)+H₂O (l)   (13)

The slurry from reactor 5826 then proceeds to a filter 5830, where theprecipitated calcium carbonate is separated from the ammonium nitrate.The calcium carbonate proceeds to a dryer 5832 to remove any remainingliquid impurities 5834. The filtrate containing ammonium nitrateproceeds to an evaporator 5836, resulting in a highly pure ammoniumnitrate solution that may be marketed as a fertilizer 5838.

The final step may include adding ammonium carbonate to form aninsoluble calcium carbonate and an ammonium nitrate solution (reaction12). The calcium carbonate may be filtered 280, washed, and then dried285 to produce a high-quality precipitated calcium carbonate product.The ammonium nitrate solution may be concentrated by evaporator 290 andmarketed as a fertilizer.

Ash Conversion Systems and Methods

Described herein are systems and methods for generating valuableproducts from coal ash with near-zero waste. The systems and methodsdisclosed herein are unique in that they are the first demonstratedsystems and methods that can convert coal ash feedstock (and othermetal-bearing feedstocks) into marketable products of high value withnear-zero waste.

The ash conversion process may begin with a leach process. A leachprocess, in some embodiments, may involve contacting, passing, and/orpercolating an acid through a feedstock. In some embodiments, the leachprocess may be performed in one or more stages using one or moredifferent acids or different concentrations of the same acids. In anexemplary embodiment, the leach process is performed in two-stages usingdifferent concentrations of hydrochloric acid.

In some embodiments, elements and/or compounds in the leachate resultingfrom the leach process in the ash conversion process may then beseparated by selective precipitation at one or more different pHs. pHadjustments may be made to the leachate using a base such as calciumhydroxide (lime) or sodium hydroxide (caustic), or both in separatesteps. Potassium and ammonium hydroxides are other possible bases thatmay be utilized for pH adjustment of the leachate. After eachprecipitation, the precipitate is separated by filtration and thefiltrate proceeds to the next pH adjustment and precipitation. In someembodiments, one or more hydroxides of iron, aluminum, misch metals(rare earth elements (REEs) and transition metals), magnesium, andcalcium may be separated sequentially. In some embodiments, theseparations may achieve high purities greater than 90%. Depending on thebase(s) used in pH adjustments to the leachate, the final liquor at theend of the ash conversion process may comprise high-purity sodiumchloride, resulting in near-zero waste streams. The pH adjustmentsdescribed herein may be equally applied to the FGD conversion processdescribed above.

FIGS. 18 through 21 depict embodiments of an ash conversion system andmethod for producing valuable products from an ash feedstock withnear-zero waste. FIGS. 18 and 19 depict a lime embodiment of the ashconversion system and method and FIGS. 20 and 21 depict a causticembodiment of the ash conversion system and method. In some embodiments,the ash feedstock may be powdered. In some embodiments, the ashfeedstock may be slurried.

Lime Embodiment

FIGS. 18 and 19 depict a lime embodiment 1800 a of the ash conversionsystem and method for producing valuable products from an ash feedstockwith near-zero waste. In the depicted embodiment, ash feedstock is firstfloated with water in a flotation tank 1805 to remove microspheres (alsocalled cenospheres), which can be marketed as a product. In someembodiments, microspheres may make up 1-2 wt % of the ash feedstock. Themicrospheres may be composed primarily of aluminosilicates. Themicrospheres are hard and hollow, lightweight, waterproof, innoxious,and insulative. This makes them highly useful in a variety of products,notably fillers. The microspheres are also used as fillers in cement toproduce low-density concrete.

The remainder of the ash feedstock, with optional solids recycle from asilica fusion process depicted in FIG. 50 , proceeds to leach tank 1810in leach process 1811. Leaching may be completed in one or two stagesusing one or more different acids or different concentrations of thesame acids resulting in leached ash feedstock. In some embodiments,leaching may be performed in two-stages with hydrochloric acid (HCl) ofdiffering concentrations. The leach process 1811 is disclosed in moredetail using examples and experimental data under the Examples headingand in FIG. 35 .

Still referring to FIG. 18 , the leached ash feedstock is separated insolid/liquid separator 1815 resulting in solids, comprising silica andother impurities in some embodiments, and liquor. The solids may proceedto either FIG. 49 or FIG. 50 for further processing. The liquor fromsolid/liquid separator 1815, along with optional liquor recycle fromFIG. 49 proceeds to a pH adjustment tank 1820 where pH is adjusted toprecipitate particular components. In the depicted embodiment, the pH isfirst adjusted from less than 1 to pH 1 using calcium carbonate (CaCO₃)then to between pH 2.5 to 3 using calcium hydroxide (Ca(OH)₂ or lime).The calcium carbonate may be sourced from the FGD conversion processdescribed above and shown in FIG. 2 . Hydrogen peroxide (H₂O₂) may alsobe added to the pH adjustment tank 1820 to convert ferrous iron toferric iron. The pH adjusted solution from pH adjustment tank 1820proceeds to solid/liquid separator 1825 resulting in solids comprisingpredominantly iron hydroxide (Fe(OH)₃) precipitate and liquor. TheFe(OH)₃ may be marketed as-is or calcined in an oven 1830 (at 300° C.,in some embodiments) with air circulation to ferric oxide (alpha-Fe₂O₃).The liquor from solid/liquid separator 1825 proceeds to a second pHadjustment tank 1835 where the pH is adjusted to pH 4 using Ca(OH)₂, inthe depicted embodiment. The pH adjusted solution from pH adjustmenttank 1835 proceeds to solid/liquid separator 1840 resulting in solidscomprising predominantly aluminum hydroxide (Al(OH)₃) and liquor. TheAl(OH)₃ can be marketed as-is or calcined in an oven 1845 (at 250° C.,in some embodiments) to alumina (Al₂O₃). The liquor from solid/liquidseparator 1840 proceeds to a third pH adjustment tank 1850 where the pHis adjusted to pH 8 using Ca(OH)_(2,) in the depicted embodiment. The pHadjusted solution from pH adjustment tank 1850 proceeds to FIG. 19 .

FIG. 19 is a continuation of FIG. 18 . The pH adjusted solution from thethird pH adjustment tank 1850 proceeds to solid/liquid separator 1855resulting in solids comprising predominantly rare earth hydroxides andsome transition metals. The transition metals and rare earth hydroxidesmay be sold as-is or may proceed to further separation/processingdisclosed in more detail under the Products heading. The liquor fromsolid/liquid separator 1855 proceeds to a fourth pH adjustment tank 1865where the pH is adjusted to pH 10.5 to 11 using Ca(OH)₂, in the depictedembodiment. The pH adjusted solution from pH adjustment tank 1865proceeds to solid/liquid separator 1870 resulting in solids comprisingpredominantly magnesium hydroxide (Mg(OH)₂) and liquor. The Mg(OH)₂ maybe marketed as-is or may be calcined in an oven 1875 (at 250° C., insome embodiments) to magnesium oxide (MgO). The liquor from solid/liquidseparator 1870, which contains calcium ions, proceeds to precipitationtank 1880 where a stoichiometric amount of sodium carbonate (Na₂CO₃) isadded to precipitate calcium carbonate. The solution from theprecipitation tank 1880 proceeds to solid/liquid separator 1885resulting in solid calcium carbonate (CaCO₃) and a liquor. The totalcalcium carbonate produced is the sum of the calcium in the ash feedplus the lime reagent (Ca(OH)₂) used for pH adjustment. The liquor fromsolid/liquid separator 1885 proceeds to an acid neutralization tank 1890where the hydroxides used in the solid/liquid separation steps (1815,1825, 1840 FIGS. 18 and 1855, 1870, 1885 FIG. 19 ) are neutralized to pH7 with HCl. The final product is sodium chloride (NaCl) and may bemarketed as a solution (brine) or the NaCl salt may be crystallized outof the solution using a crystallizer or spray dryer (not depicted).

Caustic Embodiment

The caustic embodiment 100 b (FIGS. 20 and 21 ) of the ash conversionprocess may comprise essentially the same steps and equipment as thelime embodiment 100 a (FIGS. 18 and 19 ) of the ash conversion processwith the primary difference being the reagent used in the pH adjustmentsteps. In the caustic embodiment, caustic (sodium hydroxide, or NaOH) isused in place of lime (Ca(OH)₂) in the pH adjustment steps. In someembodiments, the NaOH concentration may be 20 wt %.

FIGS. 20 and 21 depict a caustic embodiment 1800 b of the ash conversionsystem and method for producing valuable products from an ash feedstockwith near-zero waste. In the depicted embodiment, ash feedstock may befloated with water in flotation tank 1805 to remove microspheres, whichmay be marketed as a product as mentioned above. In some embodiments,microspheres make up 1-2% of the ash feedstock. The remainder of the ashfeedstock, with optional solids recycle from a silica fusion processdepicted in FIG. 50 , may proceed to leach tank 1810 in leach process1811. Leaching may be completed in one or two stages using one or moredifferent acids or different concentrations of the same acids resultingin leached ash feedstock. In some embodiments, leaching is performed intwo-stages with hydrochloric acid (HCl) of differing concentrations. Theleach process 1811 is disclosed in more detail using examples andexperimental data under the Examples heading and in FIG. 35 .

Still referring to FIG. 20 , the leached ash feedstock may be separatedin solid/liquid separator 1815 resulting in solids, comprising silicaand other impurities in some embodiments, and liquor. The solid residuesfrom the leaching process may proceed to either FIG. 49 or FIG. 50 forfurther processing. The liquor from solid/liquid separator 1815, alongwith optional liquor recycle from FIG. 49 may proceed to a pH adjustmenttank 1820 where pH is adjusted to precipitate particular components. Inthe depicted embodiment, the pH is adjusted to 2.5-3 using NaOH.Hydrogen peroxide (H₂O₂) may also be added to the pH adjustment tank1820 to convert ferrous iron to ferric iron. The pH adjusted solutionfrom pH adjustment tank 1820 may proceed to solid/liquid separator 1825resulting in solids comprising predominantly iron hydroxide (Fe(OH)₃)precipitate and liquor. The Fe(OH)₃ may be marketed as-is or calcined inan oven 1830 (at 300° C., in some embodiments) with air circulation toiron oxide (alpha-Fe₂O₃). The liquor from solid/liquid separator 1825may proceed to a second pH adjustment tank 1835 where the pH is adjustedto pH 4 using NaOH, in the depicted embodiment. The pH adjusted solutionfrom pH adjustment tank 1835 may proceed to solid/liquid separator 1840resulting in solids comprising predominantly aluminum hydroxide(Al(OH)₃) and liquor. The Al(OH)₃ can be marketed as-is or calcined inan oven 1845 (at 250° C., in some embodiments) to alumina (Al₂O₃). Theliquor from solid/liquid separator 1840 may proceed to a third pHadjustment tank 1850 where the pH is adjusted to pH 8 using NaOH, in thedepicted embodiment. The pH adjusted solution from pH adjustment tank1850 may proceed to FIG. 21 .

FIG. 21 is a continuation of FIG. 20 . The pH adjusted solution from thethird pH adjustment tank 1850 may proceed to solid/liquid separator 1855resulting in solids comprising predominantly rare earth hydroxides andsome transition metals. The transition metals and rare earth hydroxidesmay be sold as-is or may proceed to further separation/processingdisclosed in more detail under the Products heading. The liquor fromsolid/liquid separator 1855 may proceed to a fourth pH adjustment tank1865 where the pH is adjusted to pH 10.5 to 11 using NaOH, in thedepicted embodiment. The pH adjusted solution from pH adjustment tank1865 proceeds to solid/liquid separator 1870 resulting in solidscomprising predominantly magnesium hydroxide (Mg(OH)₂) and liquor. TheMg(OH)₂ may be marketed as-is or may be calcined in an oven 1875 (at250° C., in some embodiments) to magnesium oxide (MgO). The liquor fromsolid/liquid separator 1870 may proceed to a fifth pH adjustment tank1880 where the pH is adjusted to between 12.5-13 using NaOH, in thedepicted embodiment. The pH adjusted solution from pH adjustment tank1880 proceeds to solid/liquid separator 1885 resulting in solid calciumhydroxide (Ca(OH)₂) and liquor. In some embodiments, sodium carbonatemay be added to the liquor from 1885 to precipitate traces of barium andstrontium before neutralization in tank 1890. The Ca(OH)₂ may beconverted to calcium carbonate (CaCO₃) with the addition of CO_(2.) Theliquor from solid/liquid separator 1885 may proceed to an acidneutralization tank 1890 where the hydroxides used in the solid/liquidseparation steps (1815, 1825, 1840 FIGS. 20 and 1855, 1870, 1885 FIG. 21) are neutralized to pH 7 with HCl. The final product is sodium chloride(NaCl) and may be marketed as a solution (brine) or the NaCl salt may becrystallized out of the solution using a crystallizer or spray dryer(not depicted). In some embodiments of the caustic flowsheet, the finalcalcium precipitation is not performed, and the final product is asodium chloride/calcium chloride blend.

Process Equipment Options

As used herein, “filter” and “solid/liquid separator” or “separator” areused interchangeably. The solid/liquid separators depicted in FIGS. 18through 21 may be any one or more of centrifuges, disc, pan, belt, ordrum filters, or other solid/liquid separators known in the art. To helpcoagulation of the precipitate and ease filtration, techniques such asheating or seeding with recycled product (10-30 wt %) could be used.Calciner temperatures may be between 250° C. and 300° C. Materialtransfer between processes/equipment may be carried out with the use ofpumps, etc.

As used herein, “reactor” is used interchangeably with “leach tank”, “pHadjustment tank”, “acid neutralization tank”, “dissolver”, and any otherterm for an apparatus within which a chemical reaction takes place. Areactor may be a tank reactor, a batch reactor, a continuously stirredtank reactor, a plug-flow reactor (sometimes also referred to as anin-line reactor), or any other reactor known in the art.

Feedstocks

The ash conversion systems and methods disclosed herein are capable ofbeing applied to waste streams other than coal ash such as red mud wastefrom the bauxite (comprising primarily Fe₂O₃, Al₂O₃, and SiO_(2,) andminor amounts of CaO, Na₂O, TiO, K₂O and MgO) in the synthesis ofaluminum, slag from the steel furnaces (comprising CaO, SiO₂, Al₂O₃,FeO, and MgO), municipal incinerator solid waste, acid mine drainage,mine tailings, and other metal bearing waste streams, because of theirsimilar compositions. Each waste stream may require a different acidcomposition to achieve the best dissolution as was described in thevarious acids' formulations (FIGS. 25 to 29 ) that were tested for coalash. Some variations in type and composition of feedstock may requireadditional or fewer processing steps. In some embodiments, feedstock mayrequire grinding to reduce particle size prior to processing in the ashconversion process. The feedstock may be in powder form wherein powderis a bulk solid composed of many very fine particles. In someembodiments, the feedstock may need to be dispersed in slurry prior toprocessing in the ash conversion process. In still other embodiments,the feedstock may be a slurry of metal-bearing solids suspended inliquid.

Depending on the composition of the ash feedstock, residues may not havecarbon impurities or may comprise other impurities. The silica residuemay be calcined at 600° C. or higher to burn off all the carbonresulting in an off-white silica product with potentially improvedmarket value over silica containing carbon impurities. These finalresidues can be further purified by an additional leaching in 30 wt %HCl for 24 hours. The leachate may be combined with the other leachatesand recycled through the ash conversion process, in some embodiments.

Products

The products are generally 1) silica, 2) ferric oxide, 3) aluminumoxide, 4) a mixture of REE and transition elements that are concentratedbetween 20 to 100-fold from the original coal ash, 5) magnesium oxide,6) calcium carbonate, and 7) sodium chloride. The oxides originallyprecipitate as hydroxides and may optionally be marketed as such. Insome embodiments, the hydroxides may be converted to carbonates usingreactants such as carbon dioxide. In some embodiments, manganese mayadditionally be precipitated at a pH of 9.

The leach residue from solid/liquid separator 1815 (FIGS. 18 and 20 )may predominantly include amorphous and crystalline silica, technicalgrade, which has commercial applications. Commercial applications forsilica include additives in tires, elastomers, and plastics; in theconstruction industry as an anti-caking agent; for sand casting formanufacture of metallic components; and for use in glassmaking andceramics. The value of silica generally improves with higher purity,smaller particle size, and larger surface areas. With some ashfeedstocks, the silica also contains some aluminum silicate such asfibrous mullite or high aspect ratio mullite. This mullite could haveits own intrinsic high value for uses in high temperature applications,such as in ceramic-in-ceramic fiber reinforcements for ceramic enginesand turbine components. The characteristic formation of fibrous mullitein fly ash (FIG. 60 ) is the only potentially large volume source forthis valuable form of mullite. Post process of the silica/mulliteresidue from ash processing can be separated by dissolving the silica[which can be reprecipitated into to a very pure silica form] and theamorphous aluminosilicate in caustic and leaving behind fibrous mulliteneedles.

Ferric oxide is used primarily as a pigment in paints, glazes, coatings,colored concrete, mulches, mordant, coating for magnetic recordingtapes, the manufacturing of polishing compounds and as an abrasive forglass, precious metals, and diamonds. An oxidizing atmosphere must beused in the oven to convert the iron hydroxide to a ferric oxide pigmentwith strong color strength.

Aluminum hydroxide is often used as a feedstock for the manufacture ofother aluminum compounds and in the manufacture of abrasives,waterproofing, water treatment, and as a filter medium. Additional usesinclude the manufacture of aluminosilicate glass, a high melting pointglass used in cooking utensils and in the production of fire clay,pottery, and printing ink. Converting the hydroxide to aluminum oxide athigh temperature produces oxides used in high value applications such aspaint, and as a filler in plastics and cosmetics.

Magnesium hydroxide is used in the wastewater treatment process; as aflame- or fire-retardant filler; as a fuel additive to treat heavy fueloils; as well as in the ceramic glazing process. Magnesium oxide is usedas an anticaking agent in foods, in ceramics to improve toughness, andin optics. Magnesium carbonate is used in fireproofing, a smokesuppressant in plastics, and a reinforcing agent in rubber.

The calcium carbonate produced is of high purity and very small particlesize and so has a plethora of uses in many diverse industries including:the oil and gas industry as drilling fluid make-up to increase the fluiddensity, as an additive to control fluid loss to formation, and theoilfield cementing industry as a loss circulation material; the buildingmaterials and construction industry for roofing shingles, tiles, cement,brick, and concrete block manufacture; and commercial applications suchas industrial filler in the paper, paint, plastics, and rubberindustries. Analysis of the precipitated calcium carbonate showed a leadvalue of 0.54 ppm, which makes it a candidate for medical and foodapplications. Lead precipitates between pH 5-8 as shown in FIG. 38 . Insome embodiments, the final drying step strongly influences the particlesize distribution of the precipitated calcium carbonate. Under normaldrying conditions, such as a rotatory dryer, the product forms largeagglomerates, even though the actual particle size when forming theprecipitated calcium carbonate is in the nanoparticle range (FIG. 59 ).Because agglomerates are formed in conventional drying processes, postprocessing may be necessary to break up the agglomerates by using adeagglomerator, such as a ball mill.

In some embodiments, rather than drying and deagglomerating the calciumcarbonate, a slurry of the calcium carbonate product may be spray driedor dried using a Swirl Fluidizer. Both of these techniques yield a driedproduct of small particle size in a single step without the need for adeagglomeration step.

Sodium chloride solution is used in a myriad of industrial applications.It is used in the chlor-alkali process, the process to produce chlorineand sodium hydroxide (see Examples for more detail). It is also widelyused as a de-icing and anti-icing agent in winter climate roadapplications and as a dust suppressant in many mining operations.Crystallization of sodium chloride solution will produce dry sodiumchloride crystals, commonly referred to as salt. Sodium chloridecrystals are used across oil and gas exploration activities as anadditive to drilling fluids as well as cementing operations, in the pulpand paper industry as a bleaching product for wood pulp, in the watersoftening industry, swimming pool chemical industry as pool salt and ina great number of other industrial applications.

Precipitation

FIG. 36 shows a chart depicting cumulative precipitation percent versuspulp pH for class C ash. Iron is best separated at pH 2.5 to 3 tominimize the amount of aluminum impurities. Aluminum is thenprecipitated at pH 4. The precipitation of some of the rare earths isshown in FIG. 37 . As can be seen in FIG. 37 , scandium precipitateswith iron while most of the other REEs precipitate between pH 5 and pH9. At pH 9, manganese may also be precipitated. Magnesium can beseparated at pH 10.5-11 and calcium at pH 13. FIG. 38 is a tabledepicting the percent composition of precipitate hydroxides at differentpHs resulting from precipitation testing.

In some embodiments, after each pH condition, the liquor may be filteredto separate a product and the filtrate is then subjected to the next pHcondition. The precipitates for iron and aluminum may be difficult tofilter with simple vacuum, but that may be facilitated by high speedcentrifugation. Another approach may be to seed the precipitation with10-30% recycled product to produce more easily filterable solids(precipitate).

FIGS. 39 through 45 depict the percent elements precipitated at each pHcut for class C ash feedstock. FIG. 39 depicts percent elementsprecipitated at pH 3. FIG. 40 depicts percent elements precipitated atpH 4. FIG. 41 depicts percent elements precipitated at pH 5-8. FIG. 42depicts percent elements precipitated at pH 5-8 with aluminum removed toshow the smaller percentages more clearly. FIG. 43 depicts percentelements precipitated at pH 9. FIG. 44 depicts percent elementprecipitated at pH 10. FIG. 45 depicts percent elements precipitated atpH 2.5. The iron purity shown precipitated at pH 3 can be improved to92.5 wt % by carrying out the precipitation at pH 2.5.

The percent element precipitated at pH 13 is >99% calcium. The remainingliquor is not a waste stream but a sodium chloride solution containingtraces of strontium and barium. These can be precipitated with sodiumcarbonate to isolate high value products. The concentrations are 151 ppmstrontium and 2 ppm barium. Since the solution is at pH 13, the excesshydroxide must be neutralized with HCl to pH 7 for the final product.The final product waste composition of the sodium chloride is shown inFIG. 46 .

The final liquor is a clean sodium chloride solution containing tracesof strontium and barium when using sodium hydroxide as the base. It maybe further purified by adding sodium carbonate to precipitate strontiumand barium carbonates. At the end of this process, a sodium chloridesolution remains that can be marketed as a brine or dried to the salt.It should be noted that barium sulfate is mostly insoluble in thelixiviant, so most of it remains in the residue.

This final sodium chloride product is an important aspect of thisdisclosure, which processes ash with minimal waste. This is a surprisingresult compared to previous attempts to separate products from CCP. Forevery 1 ton of ash feedstock this disclosure generates 0.8 tons of NaCl.There is a market for this product as a solution or as a dried solid.

An alternative process embodiment is the use of calcium carbonate(CaCO₃) and calcium hydroxide (Ca(OH)₂) as the reagent forprecipitation. Calcium carbonate may be used at the lower pHs up topH 1. After that, Ca(OH)₂ may be used. FIG. 47 shows the precipitationas a function of pH for this reagent. FIG. 48 shows the elementalcomposition of all the precipitated products from Ca(OH)₂ precipitationtesting.

Product Enhancements Silica

In some embodiments, the residue after the leach process 1811 (FIGS. 18and 20 ) is silica which may comprise up to 20% impurities comprisingprimarily aluminum and carbon and occasionally barium in the testexamples. In some embodiments, impurities may be removed by at least oneof calcining, caustic fusion and filtration. Carbon impurities, forinstance, may be removed by calcining at 600° C. or higher (FIG. 49 ).

In preliminary testing, two methods of caustic fusion were found to besuccessful: the first was a 300° C. fusion with caustic (FIG. 50 ) whilethe other was a dissolution in 8M NaOH at 90° C. The first methoddissolved 68% of the residue while the second yielded 62%. However, the8M NaOH dissolved less aluminum than the caustic fusion process. Thedissolution of the silica residue can be greatly increased using highertemperatures closer to 1000° C. up to 1200° C. Caustic may be sodium orpotassium hydroxide.

The reactions are shown below in equations (14) and (15):

2NaOH+SiO₂→Na₂SiO₃+H₂O   (14)

Al₂SiO₅+4NaOH→2NaAlO₂+Na₂SiO₃+2H₂O   (15)

The sodium silicate formed from the fusion may be dissolved in water andthe mixture filtered to remove any insoluble impurities. In someembodiments, the solids may be recycled back to the flotation tank 1805or to the leach tank 1810 (FIGS. 18 and 20 ).

In some embodiments, the filtrate may be treated with HCl to drop the pHto at least 1 and precipitate silicic acid (H₄SiO₄). In someembodiments, the silicic acid may be filtered and then calcined, orspray dried then calcined, to convert it a high purity (greater than99%), high value amorphous silica powder. In some embodiments, thesilica powder has a BET-N2 surface area of greater than 160 m²/g, whichhas numerous applications as an additive in tires, elastomers, plastics,and rubber products. The thermal decomposition of silicic acid tosilicon dioxide and water is shown in equation (16):

H₄SiO₄→SiO₂+2H₂O   (16)

In preliminary testing, a purity of 95.4% was obtained with the fusionproduct. In some embodiments, the filtrate may be an acidic solution ofsodium chloride containing some elements such as aluminum and may berecycled back to the beginning of the process (FIGS. 18 and 20 , pHadjustment tank 1820).

Another option is to add sodium hydroxide to bring the solution's pH to4 and precipitate aluminum hydroxide. The hydroxide may then be calcinedto the oxide product. The remaining liquor is sodium chloride product asin the caustic and lime flowsheets the (FIGS. 19 and 21 ).

Process Embodiments for Silica Processing

FIGS. 49 and 50 depict two options for further processing of a silicaproduct as optional continuations of FIGS. 18 and 20 . FIG. 49 depictsan acid dissolution process 4900 and FIG. 50 depicts a sodium hydroxidefusion process 5000. In FIG. 49 , residue silica and silicates fromsolid/liquid separation 1815 (FIGS. 18 and 20 ) proceed to dissolutiontank 4905. In some embodiments, 30% hydrochloric acid (HCl) is appliedfor 24 hours in dissolution tank 4905. Following acid dissolution indissolution tank 4905, the liquor proceeds to solid/liquid separator4910 resulting in solids and a liquor. In embodiments where the solidscomprise carbon, the solids proceed to an oven 4915 for carbon burnoff.In some embodiments, the solids may be heated in an oven 4915 for 6hours at a minimum of 600° C. resulting in a purified silica (SiO₂)product. The liquor from solid/liquid separator 4910 may be recycled tothe pH adjustment tank 1820 (FIGS. 18 and 20 ).

In FIG. 50 , residue silica and silicates from solid/liquid separation1815 (FIGS. 18 and 20 ) proceed to sodium hydroxide (NaOH) fusion 5002(at 300° C. in some embodiments). Potassium hydroxide may be usedinstead of NaOH, in some embodiments. Water may be added to the fusedmaterial to produce a liquor, which proceeds to solid/liquid separation5005. Solids may optionally proceed to the leach tank 1810 (FIGS. 18 and20 ) to recycle impurities, where impurities are dependent on thecomposition of the feedstock. The filtrate proceeds to acidificationtank 5010 where acid, 6M HCl in the depicted embodiment, is added toreduce the pH of the filtrate to 1. The pH adjusted liquor proceeds tosolid/liquid separation 5015. The solids are primarily silicic acid(H₄SiO₄) precipitates which may proceed to at least one of oven 5020, at250° C. in the depicted embodiment, and spray calcination 5025 resultingin a high purity (greater than 99 wt %) amorphous SiO₂ product. The SiO₂product may be powdered in some embodiments. Spray drying may preservethe small particle size and prevent agglomeration. In some embodiments,the particles may have submicron diameters. The liquor proceeds toprecipitation tank 5030. In the depicted embodiment, 1M NaOH is added tothe precipitation tank 5030 to raise pH of the liquor above 7. Theliquor proceeds to solid/liquid separation 5035. The solids areprimarily aluminum hydroxide (Al(OH)₃) which may be marketed as-is orcalcined in oven 5040, at 250° C. in the depicted embodiment, resultingin an alumina (Al₂O₃) product. The final liquor is sodium chloride(NaCl) which can be marketed as a product. This process can also be usedto recover aluminum and silica from any number of aluminosilicate oresfeedstocks or industrial waste streams.

Material transfer between processes/equipment may be carried out withthe use of pumps, etc.

Iron and Aluminum

Iron hydroxide may be precipitated together with scandium and otherheavy elements. Aluminum hydroxide is precipitated next with some ironimpurity and other minor elements. In some embodiments, the ironhydroxide and the aluminum hydroxide are both around 90% pure but arecontaminated with a small amount of the other product. These productsmay be further purified by first dissolving them in excess NaOH at 90°C. The aluminum hydroxide dissolves to form a soluble aluminate whichcan then be separated from the iron hydroxide. After the solid-liquidseparation, the aluminum can be reprecipitated by adding acid to getback to the insoluble hydroxide.

Manganese

In some embodiments, minor levels of manganese (0.02-0.03 wt %) may beseparately precipitated in either the caustic or the lime processes ofFIGS. 18 through 21 at a pH of 9. The major impurity is magnesium.

Barium and Strontium

In some embodiments of the process depicted in FIGS. 20 and 21 , afterthe calcium is precipitated as calcium hydroxide, sodium carbonate canbe added to separate barium and strontium carbonates before the finalliquor is neutralized to yield sodium chloride.

REEs and Transition Metals

In some embodiments, rare earth elements (REEs) and transition metalsmay be separated from each other using ion exchange, solvent extraction,adsorption, or a combination thereof. In some embodiments, the processmay concentrate REEs and transition metals into a rare-earth mischmetalfrom 20 to 100-fold. As used herein, “rare-earth mischmetal” refers to amixed metal alloy of rare-earth elements. In some embodiments,rare-earth mischmetal may comprise at least one of cerium, lanthanum,and neodymium. In some examples, a rare-earth mischmetal compositionincludes approximately 55% cerium, 25% lanthanum, and 15-18% neodymiumwith other rare earth metals following. The mischmetals may be marketedas-is to vendors specializing in separating these products, or they maybe treated in a separate process.

Chlor-Alkali

A synergy exists between the process depicted in FIGS. 18 through 20 anda chlor-alkali plant. The sodium chloride product from FIGS. 19 and/or21 may be used as feed to a chlor-alkali plant, and a discounted supplyof hydrochloric acid may be used in one or more leaching steps.

Embodiment A

Some embodiments use the well-established technology of a chlor-alkaliplant to convert sodium chloride rich final product from FIG. 19 and/or21 to sodium hydroxide, hydrogen, and chlorine. Hydrogen and chlorineare then combined to produce HCl gas, which is then dissolved in waterto produce hydrochloric acid. By recycling the sodium chloride finalprocess stream to replenish the starting reagent materials, hydrochloricacid and sodium hydroxide, a significant savings may be achieved at thecost of capital investment in a chlor-alkali plant. In some embodiments,hydrochloric acid is used as the leaching agent in FIGS. 18 and/or 20and sodium hydroxide can be used directly in the caustic flowsheetembodiment 1800 b (FIGS. 20 and 21 ) or converted to sodium carbonate bybubbling CO₂ (exhaust gas from a fossil fuel power plant, in someembodiments) into sodium hydroxide to be used as a reagent toprecipitate a CaCO₃ product in the lime flowsheet embodiment 1800 a(FIGS. 18 and 19 ). In some embodiments, the CaCO₃ product is highpurity (>99 wt %).

Embodiment B

Some embodiments may use a side stream from a fossil fuel plant gaseousdischarge containing carbon dioxide (CO₂) to use directly in theprocess, thereby saving a significant reagent cost in purchased CO₂ gasand at the same time achieving an environmental benefit by capturing agreenhouse gas into commercial products (carbonates).

One of the reactions used to capture the CO₂ is absorbing it in sodiumhydroxide from the chlor-alkali plant to form sodium carbonate, whichmay be used as a process reagent in some embodiments. The acid-basereaction is rapid; in some embodiments, the reaction may be monitored bytracking the pH from the higher sodium hydroxide value to the lowersodium carbonate value. This conversion can be done in a batch mode or acontinuous mode through pipes with one or more CO₂ entry points to reactwith the caustic to quantitatively produce sodium carbonate and save thecost of another purchased reagent. In other embodiments, the CO₂ may beabsorbed into ammonium hydroxide produced from dissolving ammonia inwater. The lower cost of the ammonia, and the smaller amount requiredfor the reaction, may result in a significant cost savings versus usingsodium hydroxide or potassium hydroxide. This produces the samehigh-quality precipitated calcium carbonate and ammonium chloride orpotassium chloride by-products, which are also fertilizers. If nitricacid or phosphoric acids are used early in the process, then theproducts are ammonium nitrate and potassium nitrate, or ammoniumphosphate and potassium phosphate, respectively. Each of these productsis a better fertilizer than ammonium chloride or potassium chloride;however, ammonium nitrate and potassium nitrate are more hazardous, asthey are strong oxidants.

In some embodiments, CO₂ may be provided from other processes, plants,or sources. In some embodiments, naturally occurring or stored CO₂ maybe pumped from underground formations. Any source of carbon dioxidecould be beneficially used for carbon sequestration from a slip streamoff of a coal power plant exhaust.

Process Control

In some embodiments, one or more processors may be used to control andmanage one more aspects of the systems and methods disclosed herein.

Disclosed herein are systems and methods for processing a metal-bearingwaste streams. In some embodiments, the feedstock is a powder thatcomprises metal-bearing components and sulfur components. The feedstockmay be loaded into a first reactor to begin processing. In someembodiments, a processor is configured to operate a processing sequencecomprising at least one of a dissolution process and a precipitationprocess wherein the dissolution process and/or precipitation processtake place in one or more reactors. The processor may be configured toperform one or more of the following steps: using a first dissolutionprocess, wherein the first dissolution process comprises using a leachprocess performed by at least one of contacting, passing, andpercolating an acid through the powder feedstock and collecting aleachate formed in a second reactor; responsive to collecting theleachate, use a sequential selective precipitation process at apredetermined pH to sequentially precipitate components, wherein a firstpredetermined pH is used to precipitate a first component from theleachate; responsive to precipitating the first component, separate byfiltration the first component, and collect the first filtrate in atleast one of the second reactor and a third reactor; responsive tocollecting the first filtrate, use a base component to adjust the firstfiltrate to a second predetermined pH; using the sequentialprecipitation process at the second predetermined pH, precipitate asecond component, separate by filtration the second component andgenerate a second filtrate; and using the sequential precipitationprocess to separate additional components based on the predetermined pHsof the component of interest. The steps may be performed in orders otherthan the order presented herein and additional or fewer steps may beperformed. In some embodiments, the processor is configured to use touse a predetermined pH to separate components from the leachate based onpredetermined logic.

Non-Transitory Computer Readable Medium

The systems and methods described above can use dedicated processorsystems, micro controllers, programmable logic devices, ormicroprocessors that perform some or all of the communicationoperations. Some of the operations described above may be implemented insoftware and other operations may be implemented in hardware.

The systems and methods described above can use dedicated processorsystems, micro controllers, programmable logic devices, ormicroprocessors that perform some or all of the communicationoperations. Some of the operations described above may be implemented insoftware and other operations may be implemented in hardware.

The various operations of methods described above may be performed byany suitable means capable of performing the operations, such as varioushardware and/or software component(s), circuits, and/or module(s).

The various illustrative logical blocks, modules, and circuits describedin connection with the present disclosure may be implemented orperformed with a hardware processor, a digital signal processor (DSP),an application specific integrated circuit (ASIC), a field programmablegate array signal (FPGA) or other programmable logic device (PLD),discrete gate or transistor logic, discrete hardware components, orcombinations thereof designed to perform the functions described herein.A hardware processor may be a microprocessor, commercially availableprocessor, controller, microcontroller, or state machine. A processormay also be implemented as a combination of two computing components,e.g., a combination of a DSP and a microprocessor, a plurality ofmicroprocessors, one or more microprocessors in conjunction with a DSPcore, or any other such configuration.

In one or more aspects, the functions described may be implemented insoftware, firmware, or any combination thereof executing on a hardwareprocessor. If implemented in software, the functions may be stored asone or more executable instructions or code on a non-transitorycomputer-readable storage medium. A computer-readable storage media maybe any available media that can be accessed by a processor. By way ofexample, and not limitation, such computer-readable storage media cancomprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage,magnetic disk storage or other magnetic storage devices, or any othermedium that can be used to store executable instructions or otherprogram code or data structures and that can be accessed by a processor.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and Blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims. Processes orsteps described in one implementation can be suitably combined withsteps of other described implementations.

Certain aspects of the present disclosure may comprise a computerprogram product for performing the operations presented herein. Forexample, such a computer program product may comprise a computerreadable storage medium having instructions stored (and/or encoded)thereon, the instructions being executable by one or more processors toperform the operations described herein.

Software or instructions may be transmitted over a transmission medium.For example, if the software is transmitted from a website, server, orother remote source using a coaxial cable, fiber optic cable, twistedpair, digital subscriber line (DSL), or wireless technologies such asinfrared, radio, and microwave, then the coaxial cable, fiber opticcable, twisted pair, DSL, or wireless technologies such as infrared,radio, and microwave are included in the definition of transmissionmedium.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a terminaland/or base station can obtain the various methods upon coupling orproviding the storage means to the device.

For the sake of convenience, the operations are described as variousinterconnected functional blocks or distinct software modules. This isnot necessary, however, and there may be cases where these functionalblocks or modules are equivalently aggregated into a single logicdevice, program or operation with unclear boundaries. In any event, thefunctional blocks and software modules or described features can beimplemented by themselves, or in combination with other operations ineither hardware or software.

To facilitate the understanding of the embodiments described herein, anumber of terms are defined below. The terms defined herein havemeanings as commonly understood by a person of ordinary skill in therelevant art. Terms such as “a,” “an,” and “the” are not intended torefer to only a singular entity, but rather include the general class ofwhich a specific example may be used for illustration. The terminologyherein is used to describe specific embodiments, but their usage doesnot delimit the disclosure, except as set forth in the claims.

Batch Process: A batch process operates in separate discrete operationsthat are connected in a stepwise fashion with the materials processedbeing fed in batches.

Catalyst: A catalyst is an agent that can either accelerate ordecelerate a chemical reaction without reacting with the reactants orproducts.

Continuous Process: A continuous process is designed to operate withoutinterruptions. The materials being processed, either bulk dry or fluids,are continuously in motion undergoing chemical reactions or subject tomechanical or heat treatment.

Rare Earth Elements (REEs): REEs are any of a group of chemicallysimilar metallic elements comprising the lanthanide series and (usually)scandium and yttrium.

Transition Elements: Transition elements are any of the set of metallicelements occupying a central block (Groups IVB-VIII, IB, and IIB, or4-12) in the periodic table, e.g., manganese, chromium, and copper.

Technologically Enhanced Naturally Occurring Radioactive Materials(TENORM): Technologically Enhanced Naturally Occurring RadioactiveMaterial (TENORM) is defined as, “Naturally occurring radioactivematerials that have been concentrated or exposed to the accessibleenvironment as a result of human activities such as manufacturing,mineral extraction, or water processing.” “Technologically enhanced”means that the radiological, physical, and chemical properties of theradioactive material have been concentrated or further altered by havingbeen processed, or beneficiated, or disturbed in a way that increasesthe potential for human and/or environmental exposures. NaturallyOccurring Radioactive Material (NORM) is defined as, “Materials whichmay contain any of the primordial radionuclides or radioactive elementsas they occur in nature, such as radium, uranium, thorium, potassium,and their radioactive decay products, such as radium and radon, that areundisturbed as a result of human activities.”

As used herein, a system with “near-zero waste” means that the vastmajority of the output streams of the system are marketable products.This may be accomplished by using a plurality of recycle streams toensure that all input streams are eventually consumed. In some examplesof the present disclosure, the system may have zero waste; statedanother way, in some examples of the present disclosure, all of theoutput streams of the system are marketable products.

EXAMPLES Examples for FGD Conversion Process

The systems and methods for the FGD gypsum conversion process disclosedherein were first developed by testing batch reactions under differentconditions to arrive at initial operating conditions for a continuousdemonstration. The following data was generated in preliminary testingwith a particular feedstock and should not be considered limiting. Otheroperating conditions are anticipated.

FGD gypsum feedstock from a typical coal power plant was used as thefeedstock in preliminary testing. The composition of the FGD gypsumfeedstock used in preliminary testing of the FGD conversion process isdepicted in FIG. 3 and the particle size analysis of the FGD gypsumfeedstock is shown in FIG. 4 . Values shown “<X” are below detectionlimits, where X is the detection limit of the equipment used in theanalysis.

Batch Process

In preliminary batch testing, FGD gypsum feedstock samples were slurriedin water at 19% by weight solids and reacted with 15 wt % ammoniumcarbonate reagent solution at ambient temperature and pressure. Highersolids samples can also be used with equivalent increases in theammonium carbonate reagent. Higher temperatures are not desirablebecause the ammonium carbonate reagent is less stable at highertemperatures. Kinetic data for varying reagent additions used inpreliminary testing of the FGD conversion process, depicted in the chartin FIG. 5 , shows that at 140%-150% stoichiometric additions of reagentsto reactants the reaction between FGD gypsum feedstock and ammoniumcarbonate worked well and after one to three hours, at atmosphericpressure and ambient temperature, produced ammonium sulfate >99.9% inthe liquor and 93-95% calcium carbonate product. Lower stoichiometricadditions take much longer to react and the reaction may not go tocompletion. When evaporated to dryness, the purity of the ammoniumsulfate was >99.7%. Assays for the crystallized ammonium sulfate productproduced in preliminary testing of the FGD conversion process aredepicted in FIG. 6 . The assay results were 99.7% or 99.9% depending onthe assay method. Values shown “<X” are below detection limits, where Xis the detection limit.

Test conditions and results of preliminary testing of the FGD conversionprocess are depicted in FIG. 7 . Calculated final product valuesgenerated in preliminary testing of the FGD conversion process aredepicted in FIG. 8 and shows very high purity ammonium sulfate. Based onthese tests, the optimum stoichiometry for the FGD conversion processwas determined to be 140% to 150% and the FGD conversion reaction wascomplete after one to three hours. From 140% to 100% stoichiometry thereaction slows down as excess reagent is decreased and completion takesimpractically long times for a commercial application. Stoichiometrylower than 100% resulted in less than 99% conversion of FGD gypsumfeedstock, while higher than 150% stoichiometric resulted in wastedreagent. Variations in the composition of the feedstock may producedifferent results.

Continuous Process

As discussed herein, the FGD conversion process may be operated in acontinuous mode. Continuous mode was demonstrated in a pilot productionplant 900, depicted in FIG. 9 , operated at an FGD gypsum feedstock feedrate of 1 kg/hr. Ammonium carbonate reagent was mixed by mixer 902 withwater in vessel 905 to produce a 15 wt % ammonium carbonate solutionthat was pumped by pump 907 into the first reactor 910, operating in anoverflow mode to three other reactors 911, 912, and 913, to providesufficient reaction time for the conversion to go to completion. In someembodiments, material may be transferred between the reactors 910, 911,912, and 913 using underflow, overflow, or a pump. The FGD gypsumfeedstock was fed as a powder from bin 920 using a screw feeder 925 tothe first reactor in the reactor cascade 922, comprising reactors 910,911, 912, and 913, where it was mixed with the ammonium carbonatesolution. The slurry is then kept in suspension by mixers 931, 932, and933 in each reactor 911, 912, and 913 to allow sufficient time for thereaction to take place. The slurry overflowed from reactor 913 into acontinuous filter 940 (alternating between two pan filters) to removethe solid calcium carbonate product (which was then washed) and theresulting filtrate, ammonium sulfate liquor, was collected in tank 945.The wash liquid was collected in tank 946.

The pilot production plant 900 depicted in FIG. 9 was operated at aconstant 20° C.±3° C. and a pH ranging between 7.5 and 8.5 for 110 hours(over the course of five days) at the following conditions:

-   -   Condition 1A: 150% of the stoichiometric quantity of reactants,        Day 1-2    -   Condition 2: 125% of the stoichiometric quantity of reactants,        Day 2    -   Condition 1A: 150% of the stoichiometric quantity of reactants,        Day 3    -   Condition 1B: 150% of the stoichiometric quantity of        reactants+catalyst, Day 3    -   Condition 3: 140% of the stoichiometric quantity of reactants,        Day 4    -   Condition 4: 150% of the stoichiometric quantity of reactants        and at double the feed rates (2kg/hr), Day 4

FIG. 10 depicts calculated gypsum conversion with changing conditions inthe pilot production plant 900 (FIG. 9 ). These tests showed that:

-   -   140%-150% stoichiometric addition of reagent with respect to the        quantity of reactants was sufficient for quantitative        conversion.    -   The catalyst addition reduced the reaction time.    -   Doubling the feed rates of FGD gypsum feedstock reduced the        reaction time.

FIG. 11 depicts discharge sulfur assays from the pilot production plant900 (FIG. 9 ). Referencing FIG. 9 , the majority of the conversion tookplace within the first two reactors 910, 911 (<1.5 hours for Conditions1A and 3; and <0.75 hours for Conditions 1B and 4). The third and fourthreactors 912, 913 provided extra time to complete the reaction for theremaining gypsum.

The purity of the ammonium sulfate product produced in preliminarytesting of the FGD conversion process was 99.9 wt % (FIG. 8 ). Thepurity of the calcium carbonate produced in preliminary testing of theFGD conversion process was 93-95 wt % (FIG. 8 ) with an average D50particle size of 44 μm. While the calcium carbonate product was of goodpurity, the small amounts of impurities tinted the product a grey to tancolor. The impurities causing the color were carbon and iron which aredependent on the impurities in the FGD gypsum feedstock. FIG. 12 depictsammonium sulfate and calcium carbonate products generated by the pilotproduction plant 900 (FIG. 9 ). FIG. 13 depicts the composition of theammonium sulfate crystal product produced in the pilot production plant900 (FIG. 9 ). Variations in FGD gypsum feedstock may produce differentresults.

Chloride Removal

An example chloride removal process used in testing is described below.The following process could be scaled according to processingrequirements. Testing was carried out at 75° C. with two water leaches.

-   -   1. First 1000 g of hot 75° C. deionized water was added in a        reactor. Next, 250 g of FGD gypsum feedstock sample was added.        The mixture resulted in a slurry. The reactor was equipped with        a lid and impellor.    -   2. The slurry was agitated for half an hour.    -   3. After half hour slurry time, the leached FGD gypsum feedstock        solids were filtered and the filtrate was collected. Filtration        properties were then recorded.    -   4. 1000 g of hot 75° C. water was added to the reactor along        with the solids from step 3. The mixture was agitated for half        an hour.    -   5. After the half hour agitation time, leached solids from step        4 were filtered and the filtrate was collected. Filtration        properties were recorded.    -   6. 25 mL of filtrate 1 (step 3) were combined with 25 mL of        filtrate 2 (step 5) and submitted for assay.    -   7. The leached FGD gypsum feedstock was dried at 95° C. or lower        until the weight did not change.    -   8. Samples were submitted for assay by inductively coupled        plasma-mass spectrometry (ICP-MS) and chloride analysis.

The results obtained on an FGD gypsum feedstock sample that containedaround 0.5% by weight chloride, showed that >99 wt % of the chloride canbe leached out using the chloride removal process. The concentration ofchloride in the wash water was 1033 ppm. The cations associated with thechloride were calcium at 894 ppm and magnesium at 166 ppm. The chloridelevel in the washed FGD gypsum feedstock was reduced to around 100 ppm.

Phosphogypsum Conversion

To demonstrate this overall process, laboratory tests at the 0.5-1 kgscale were conducted to determine the optimal pH values for theseparations. The laboratory tests were followed by a larger scale testat the 50-60 kg scale based on the results from the laboratory tests.

Experimental results showed that gypsum conversion in a batch processproduced the same results as the continuous process. Therefore, both thesmall-scale and the large-scale tests may be performed in a batch modeor in a continuous mode.

The phosphogypsum samples used were assayed for elemental compositionincluding such specific tests as needed.

A non-limiting example laboratory test processed 0.5-1 kg ofphosphogypsum through the phosphogypsum conversion process to confirmthe reaction works as well as it does with FGD. Since the PG is acidic,prior to processing, the PG slurry was neutralized to pH 7 with Ca(OH)₂or NH₄OH to react with the acidic phosphate and prevent acidicdecomposition of the ammonium carbonate reactant. The neutralized feedwas reacted with ammonium carbonate to produce ammonium sulfate crystalsand technical grade calcium carbonate, as shown in equation 13. Theimpurities in the calcium carbonate precipitate may be identified andensure that the ammonium sulfate is free from deleterious contaminants.

Next, the calcium carbonate may then be purified The first step in thatprocess is to determine the optimal pH for reaction (11) so that thecalcium is dissolved but minimizes the dissolution of the impurities.Different final pHs may be selected to optimally separate theimpurities. The pH may then be increased stepwise using calciumhydroxide or another caustic or base to sequentially precipitatedissolved impurities. If fluoride is present in the sample, calciumfluoride will precipitate at higher pHs. The various precipitates maythen be filtered out and analyzed to determine the concentrations of theseparated impurities.

Once the optimal operating conditions are confirmed, a larger scale test(50-60 kg) may be performed in order to create sufficient volumes ofeach product to enable technical evaluation, support initial performancetesting of each product, confirm reagent requirements, and develop inputto support regulatory discussions about the commercial production ofthese products from the PG feedstock.

Precipitation Testing

In precipitation testing, the liquors that resulted from leach testingwere separated into value-added, marketable products. The separation wasaccomplished by adjusting the pH of the acidic solution using sodiumhydroxide in precipitation testing. Calcium hydroxide, sodium carbonate,potassium hydroxide, or ammonium hydroxide may also be used toneutralize the acid. Sharp separations of numerous metals can beobtained by careful adjustment of the pH values. The general reaction isas follows:

MCl+NaOH→MOH (insoluble)+NaCl   (13)

wherein M is a metal or non-metal cation.

One adjustment that may be made prior to the first precipitation is toadd hydrogen peroxide to oxidize ferrous ion to ferric ion. As shown inFIGS. 18-21 the sequence of precipitates is: Fe, Al, REEs and transitionmetals, Mg, and Ca when the feedstock includes ash.

The precipitation test procedure described below is for exemplarypurposes only and should not be considered limiting:

-   -   1. 3000 mL of a leachate feed solution was added to a reactor        (all in a fumehood).    -   2. A sufficient quantity (enough to increase the pH to the        desired value) of concentrated and dilute neutralizing reagent        (NaOH or CaCO₃/Ca(OH)₂) was prepared.    -   3. The reactor was equipped with a lid and the pulp was agitated        with a mixer and an impeller. pH, temperature, and ORP probes        were used.    -   4. No heat input was required. Neutralizing base reagent was        slowly added a few grams at a time. More dilute reagent was used        closer to the target pH. Time zero occurred when the target pH        was first achieved. The target pH was held for one hour, with        additional reagent additions as required.    -   5. All reagent additions and temperature changes were recorded.    -   6. After the required test time elapsed, the net pulp weight was        recorded, the pulp was filtered and the filtrate was collected,        filtration properties (time, color, paper type, etc.) were        recorded, and the weight, specific gravity, pH and ORP were        recorded.    -   7. A displacement water wash was conducted three times with 100        mL of water.    -   8. The combined wash liquors were collected, the filtration        properties were recorded (time, color, paper type, etc.), and        the weight, specific gravity, pH, and ORP were determined.    -   9. The solids were dried at 95° C. or lower until the weight of        solids was constant.    -   10. Samples were submitted for assay as per requirements.

Precipitation testing identified target pHs (also referred to herein aspH cuts) at which one or more elements precipitated out of the leachateinto the residue. The results of this testing are shown in FIG. 36 .

Leach Process

Class F ash feedstock from Northern Appalachian coal and class C ashfeedstock from Powder River Basin Coal were used in testing of the ashconversion process to ensure wide applicability. Class C ash feedstockcontains more calcium and less silica while class F ash feedstockcontains less calcium and more silica and is more difficult to acidleach. FIGS. 22 through 24 depict the compositions (elementalcomposition as well as mineral compounds by XRD) of the class F andclass C ash feedstocks used in preliminary testing of the ash conversionprocess.

Several different acid lixiviant combinations were tested in initialleach scout testing to determine the best acid lixiviants to obtain thelargest extraction of all the elemental components in the ash feedstock,except for silica which is left as a marketable residue. The acidlixiviants used in initial leach scouting tests were nitric acid,hydrochloric acid, sulfuric acid, sulfuric with sodium fluoride andcalcium fluoride, 6N aqua regia, and strong caustic. After the initialleach scouting tests, the following leach tests were performed on bothclass F and class C ash feedstocks: 6N aqua regia (HCl & HNO₃) (FIG. 25), 6N H₂SO₄+0.006N NaF (FIG. 26 ), 6N H₂SO₄+0.05% CaF₂ (FIG. 27 ),2-stage HCl pH 1.5 then 11% HCl (FIGS. 28 ), and 2-stage HCl pH 1.5 then30% HCl (FIG. 29 ). All leach tests were performed at 90° C., a solidsratio of 14%, and five sampling times, 0.5, 1, 2, 4, and 6 hours. Theresults depicted in FIGS. 25 through 27 are for 6 hour sample times andFIGS. 28 through 29 are for four hour each stage sample times. 90° C.was the maximum temperature without boiling the solution and,theoretically, should have resulted in maximum dissolution. Allleachates and residues from leach testing were analyzed compositionallyand mineralogically.

FIG. 35 depicts a two-stage leach process 3500. This process may replacethe single stage leach process 1811 depicted in FIGS. 18 and 20 . In thetwo-stage leach process 3500, ash feedstock enters a first leach tank3510 where it is leached with acid resulting in a first leachate. Thefirst leachate proceeds to solid/liquid separator 3515 resulting in aliquor which proceeds to precipitation steps and a residue. The residueproceeds to a second leach tank 3520 resulting in a second leachate. Thesecond leachate proceeds to solid/liquid separator 3525 resulting in asilica residue or product and a liquor. The liquor from solid/liquidseparator 3525 is routed back to the first leach tank 3510. In someembodiments, the acid used in the first leach tank 3510 may be HCl tolower the pH to 1.5. In some embodiments, the acid in the second leachtank may be 11 wt %-30 wt % HCl.

X-ray Diffraction (XRD) patterns together with elemental analysis showedthe final residues from the preliminary leach tests were primarilyamorphous silica with minor amounts of crystalline silica, silicates(mullite), barite, phosphates, and titanates. The final residues frompreliminary leach tests were grey in color due to a carbon impurity.

Leach Testing

The leach test procedure described below is for exemplary purposes onlyand should not be considered limiting.

-   -   1. An initial lixiviant solution was prepared and added to a        reactor. Slowly, the ash feedstock solids were added (200 g) to        the solution a few grams at a time. The target concentration was        14% solids.    -   2. The reactor was equipped with a lid and condenser, and the        pulp was agitated with a mixer and impellor.    -   3. The pulp was heated to target temperature (90° C.) with        heating mantle or other heating method. Time zero occurred when        the target temperature was achieved.    -   4. Pulp samples of about 40 mL were collected at different time        intervals to determine the effect of time on leaching. Net        weight was recorded, the pulp was filtered, the filtrate was        collected, and key data was recorded. The solids were returned        to the reactor and the filtrate kept for assay.    -   5. After the required test time, the net pulp weight was        recorded, the pulp was filtered and the filtrate was collected.        The filtration properties (time, color, paper type, etc.) were        then recorded, and the weight, specific gravity, pH, and        oxidation reduction potential (ORP) were determined.    -   6. The residue was re-pulped with a target amount of wash water        (200 mL).    -   7. A displacement wash was conducted two to four times with 70        mL water.    -   8. The combined wash liquors were collected, the filtration        properties (time, color, paper type, etc.) were recorded, and        the weight, specific gravity, pH, and ORP were determined.    -   9. The solids were dried at 95° C. or lower until weight of        solids remained constant.    -   10. Samples were submitted for assay.

Leach test results were labeled as poor, good, or excellent. Poorresults were when less than 65% dissolution was achieved for the targetelements, good results were when 65% to 90% dissolution was achieved,and excellent results were when 90% to 100% dissolution is achieved.

FIG. 25 is a table depicting leach test results of class F and class Cash feedstocks using 3:1 6N hydrochloric acid (HCl) to 6N nitric acid(HNO₃) for 6 hours. FIG. 25 indicates good leaching results but thereaction was very vigorous and NO_(x) fumes were liberated. The 6N aquaregia was found to be effective for the more difficult to dissolve classF ash feedstock; however, the aqua regia added nitrate to the finalsodium chloride product of the ash conversion process which is not idealbecause it resulted in a sodium chloride/sodium nitrate mixture which ismore difficult to market than sodium chloride.

FIG. 26 is a table depicting leach test results of class F and class Cash feedstocks using 6N sulfuric acid (H₂SO₄) and 0.006N sodium fluoride(NaF). This reaction forms insoluble sulfates with calcium so it remainswith the insoluble silica. Class F ash feedstock dissolution was poor.

FIG. 27 is a table depicting leach test results of class F and class Cash feedstocks using 6N sulfuric acid (H₂SO₄) and 0.05% calcium fluoride(CaF₂). This testing had similar results to FIG. 26 (6N sulfuric acidand 0.006N sodium fluoride).

FIG. 28 is a table depicting leach test results of class F and class Cash feedstocks using HCl to pH 1.5 in a first stage then 11% HCl in asecond stage. The dissolution of the class C ash feedstock wasexcellent, but class F ash feedstock did not perform as well. Most ofthe calcium dissolves in the first stage at pH 1.5. There is improveddissolution at the higher acid concentration for the other majorelements. Dissolution continued to improve with time.

FIG. 29 is a table depicting leach test results of class F and class Cash feedstocks using HCl to pH 1.5 in a first stage then 30% HCl in asecond stage. The class F ash feedstock had much better dissolution at30% HCl in the second stage compared to the 11% HCl in FIG. 11 . Theclass C ash feedstock dissolution, on the other hand, only improvedslightly compared to the 11% HCl second stage in FIG. 28 . The class Fash feedstock showed that the leaching improved with time.

FIG. 30 is a table depicting leach test results for continuing thesecond stage (30% HCl) leach of FIG. 29 for class C ash feedstock for 24hours. The longer leach test time improved dissolution for all elementsand results in improved quality of silica residue.

It should be noted that better extractions were obtained by leaching forlonger times (up to 24 hours was tested) and can be used to optimize thedissolution. In theory, leaching times in excess of 24 hours arefeasible but further increases in dissolution of the elements reducesexponentially over time.

Comparisons of the leach test results between 11 wt % HCl and 30 wt %HCl on both class F and class C ash feedstocks are shown in FIGS. 31through 34 . The results for class F ash feedstock shows that the 30 wt% acid is significantly more effective than the 11 wt % acid. However,the benefit for class C ash feedstock is minor, therefore the 11% is abetter selection from a reagent consumption consideration since theacid(s) used in the leaching step need to be neutralized in the nextprocess steps with the addition of lime (FIGS. 18-19 ) or caustic (FIGS.20-21 ), in some embodiments. For a lime production plant 1800 a (FIGS.18-19 ) and a caustic production plant 1800 b (FIGS. 20-21 ), in someembodiments, concentrations of about 30 wt % HCl may be used for class Fash feedstocks and around 11 wt % HCl for class C ash feedstocks.

Having described and illustrated the principles of the systems, methods,processes, and/or apparatuses disclosed herein in a preferred embodimentthereof, it should be apparent that the systems, methods, processes,and/or apparatuses may be modified in arrangement and detail withoutdeparting from such principles. Claim is made to all modifications andvariation coming within the spirit and scope of the following claims.

What is claimed is:
 1. A method for isolating metals from chemicalprocessing comprising: forming a mixture comprising chemicalintermediates, wherein the chemical intermediates comprise at least oneof calcium, nitrates, carbonates, sulfates and metal impurities whereinthe mixture results from chemical processing, and wherein the mixturehas a pH value; responsive to forming the mixture, combining the mixtureand a first reagent to change the pH of the mixture, wherein the firstreagent is added until the pH of the mixture reaches a firstpredetermined pH value to form a first precipitate, wherein the firstprecipitate comprises at least one of a metal and a rare earth element;and responsive to forming a precipitate, removing the precipitate fromthe mixture via a filter to form a first filtrate.
 2. The method ofclaim 1, further comprising: responsive to forming a first filtratecombining the first filtrate and a second reagent to change the pH ofthe first filtrate, wherein a second reagent is added until the pH ofthe first filtrate reaches a second predetermined pH value to form asecond precipitate, wherein the second precipitate comprises at leastone of a metal and a rare earth element; and responsive to forming thesecond precipitate, removing the second precipitate from the firstfiltrate to form a second filtrate.
 3. The method of claim 1, furthercomprising: responsive to forming a first filtrate combining the firstfiltrate and a second reagent to change the pH of the first filtrate,wherein a second reagent is added until the pH of the first filtratereaches a second predetermined pH value to form a second precipitate,wherein the second precipitate comprises at least one of a metal and arare earth element; responsive to forming the second precipitate,removing the second precipitate from the first filtrate to form a secondfiltrate. responsive to forming the second filtrate, combining thesecond filtrate and a third reagent to change the pH of the secondfiltrate, wherein the third reagent is added until the pH of the secondfiltrate reaches a third predetermined pH value to form a thirdprecipitate, wherein the third precipitate comprises at least one of ametal and a rare earth element; and responsive to forming a precipitate,removing the precipitate from the second filtrate to form a thirdfiltrate.
 4. The method of claim 1, wherein the chemical processcomprises at least one of phosphogypsum processing, phosphateprocessing, coal fly ash processing, and red mud processing.
 5. Themethod of claim 1, wherein the predetermined pH value is at least one of4, 9, 11, and
 13. 6. The method of claim 1, further comprising:responsive to forming a first filtrate combining the first filtrate anda reagent to change the pH of the first filtrate, wherein a secondreagent is added until the pH of the first filtrate reaches a secondpredetermined pH value, wherein the second predetermined pH value is atleast one of 4, 9, 11, and 13, to form a second precipitate, wherein thesecond precipitate comprises at least one of a metal and a rare earthelement; and responsive to forming the second precipitate, removing thesecond precipitate from the first filtrate to form a second filtrate. 7.The method of claim 1, further comprising: responsive to forming a firstfiltrate combining the first filtrate and a reagent to change the pH ofthe first filtrate, wherein a second reagent is added until the pH ofthe first filtrate reaches a second predetermined pH value, wherein thesecond predetermined pH value is at least one of 4, 9, 11, and 13, toform a second precipitate, wherein the second precipitate comprises atleast one of a metal and a rare earth element; responsive to forming thesecond precipitate, removing the second precipitate from the firstfiltrate to form a second filtrate. responsive to forming the secondfiltrate, combining the second filtrate and a third reagent to changethe pH of the second filtrate, wherein the third reagent is added untilthe pH of the second filtrate reaches a third predetermined pH valuewherein the third predetermined pH value is at least one of 4, 9, 11,and 13, to form a third precipitate, wherein the third precipitatecomprises at least one of a metal and a rare earth element; andresponsive to forming a precipitate, removing the precipitate from thesecond filtrate to form a third filtrate.
 8. The method of claim 1,wherein the process to form the first precipitate is performed at a pHof 4, and wherein the first precipitate comprises at least one of iron,aluminum, uranium, scandium, or thorium.
 9. The method of claim 1,wherein the process to form the first precipitate is performed at a pHof 9, and wherein the first precipitate comprises at least one of a rareearth element manganese, lanthanum, praseodymium, cerium, neodymium, andyttrium.
 10. The method of claim 1, wherein the process to form thefirst precipitate is performed at a pH of 11, and wherein the firstprecipitate at least one rare earth element.
 11. The method of claim 1wherein the reagent is a base.
 12. The method of claim 1, wherein thereagent is a base, and wherein the base is at least one of sodiumhydroxide, calcium hydroxide, potassium hydroxide, ammonium hydroxide,and calcium carbonate.
 13. A system for isolating metals in a chemicalprocess comprising: a mixture comprising chemical intermediates, whereinthe chemical intermediates comprise at least one of calcium, nitrates,carbonates, sulfates and metal impurities wherein the mixture resultsfrom chemical processing, and wherein the mixture has a pH; a firstreactor to combine the mixture and a first reagent to change the pH ofthe mixture, wherein the first reagent is added until the pH of themixture reaches a first predetermined pH value to form a firstprecipitate, wherein the first precipitate comprises at least one of ametal and a rare earth element; and a first filter to remove the firstprecipitate from the first mixture, wherein the remaining liquid is afirst filtrate.
 14. The system of claim 13, further comprising: a secondreactor to combine the first filtrate and a second reagent to change thepH of the mixture, wherein the second reagent is added until the pH ofthe first filtrate reaches a first predetermined pH value to form asecond precipitate, wherein the second precipitate comprises at leastone of a metal and a rare earth element; and a second filter to removethe second precipitate from the first filtrate, wherein the remainingliquid is a second filtrate.
 15. The system of claim 13, furthercomprising: a second reactor to combine the first filtrate and a secondreagent to change the pH of the first filtrate, wherein the secondreagent is added until the pH of the first filtrate reaches a secondpredetermined pH value to form a second precipitate, wherein the secondprecipitate comprises at least one of a metal and a rare earth element;a second filter to remove the second precipitate from the firstfiltrate, wherein the remaining liquid is a second filtrate. a thirdreactor to combine the second filtrate and a third reagent to change thepH of the second filtrate, wherein the third reagent is added until thepH of the first filtrate reaches a third predetermined pH value to forma third precipitate, wherein the third precipitate comprises at leastone of a metal and a rare earth element; and a third filter to removethe third precipitate from the second filtrate, wherein the remainingliquid is a third filtrate.
 16. The system of claim 13, wherein thechemical process comprises at least one of phosphogypsum processing,phosphate processing, coal fly ash processing, and red mud processing.17. The system of claim 13, wherein the predetermined pH value is atleast one of 4, 9, 11, and
 13. 18. The system of claim 13, furthercomprising: a second reactor to combine the first filtrate and a secondreagent to change the pH of the mixture, wherein the second reagent isadded until the pH of the first filtrate reaches a first predeterminedpH value to form a second precipitate, wherein the second predeterminedpH value is at least one of 4, 9, 11, and 13, wherein the secondprecipitate comprises at least one of a metal and a rare earth element;and a second filter to remove the second precipitate from the firstfiltrate, wherein the remaining liquid is a second filtrate.
 19. Thesystem of claim 13, further comprising: a second reactor to combine thefirst filtrate and a second reagent to change the pH of the firstfiltrate, wherein the second reagent is added until the pH of the firstfiltrate reaches a second predetermined pH value to form a secondprecipitate, wherein the second precipitate comprises at least one of ametal and a rare earth element; a second filter to remove the secondprecipitate from the first filtrate, wherein the remaining liquid is asecond filtrate. a third reactor to combine the second filtrate and athird reagent to change the pH of the second filtrate, wherein the thirdreagent is added until the pH of the first filtrate reaches a thirdpredetermined pH value to form a third precipitate, wherein the thirdpredetermined pH value is at least one of 4, 9, 11, and 13, wherein thethird precipitate comprises at least one of a metal and a rare earthelement; and a third filter to remove the third precipitate from thesecond filtrate, wherein the remaining liquid is a third filtrate. 20.The system of claim 13, wherein the first predetermined pH is 4, andwherein the first precipitate comprises at least one of iron, aluminum,uranium, scandium or thorium.
 21. The system of claim 13, wherein thefirst predetermined pH is 9, and wherein the first precipitate comprisesat least one of a rare earth element, manganese, lanthanum,praseodymium, cerium, neodymium, and yttrium.
 22. The system of claim13, wherein the first predetermined pH is 11, and wherein the firstprecipitate is at least one rare earth element.
 23. The system of claim13, wherein the first reagent is a base.
 24. The system of claim 13,wherein the first reagent is a base, and wherein the base is at leastone of sodium hydroxide, calcium hydroxide, potassium hydroxide ammoniumhydroxide, and calcium carbonate.